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[vsnet-grb-info 41351] GRB 251230A: Optical Observations via Virtual Telescope Project, Italy
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43260 SUBJECT: GRB 251230A: Optical Observations via Virtual Telescope Project, Italy DATE: 25/12/30 03:16:13 GMT FROM: Gianluca Masi at Virtual Telescope Project <gianluca(a)bellatrixobservatory.org> Gianluca Masi, Virtual Telescope Project (Italy), reports: We attempted to observe the optical counterpart of GRB 251230A (Lanava et al., GCN 43252) with the 17” robotic unit available at the Virtual Telescope Project facility in Manciano, Italy, equipped with a KAF-6303E based CCD camera, its QE peaking (68%) in the red part of the spectrum. We collected four, 120-second unfiltered exposures, then we averaged them. The central time of the resulting stack was 30 Dec., 02:58:46 UTC, that is about 1.6 hours after the burst. We detected a bright object at the following position (J2000.0): R.A.: 11 59 35.38 Decl.: + 11 26 18.5 mean residuals < 0.1” on both axes R= 18.4 (assuming R-mags from Gaia DR2 for the reference stars). This position is consistent with Lanava et al. (GCN 43252), Li et al. (GCN 43255) and Busmann et al. (GCN 43258). View this GCN Circular online at https://gcn.nasa.gov/circulars/43260. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41350] EP251230a / GRB 251230A: Einstein Probe detection of an X-ray transient
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43259 SUBJECT: EP251230a / GRB 251230A: Einstein Probe detection of an X-ray transient DATE: 25/12/30 02:47:03 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> B.T. Wang (YNAO, CAS), J. P. Chen (SYSU), D. Zhu, K. J. Zhang (YNU),and Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP251230a. The transient triggered EP-WXT (ID: 01709250693) at 2025-12-30T01:22:21 (UTC). The WXT position of the source is R.A. = 179.881 deg, DEC = 11.427 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 179.8996 deg, DEC = 11.4361 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). No significant X-ray source is detected within the 20 arcsec radius of the EP-FXT position. The position of FXT is 10.1 arcsec from Swift/XRT detection of GRB 251230A (Lanava et al., GCN 43252), and 11.6 arcsec from its optical counterpart (Li et al., GCN 43255). Further information will be updated when the telemetry data is received. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/43259. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41349] GRB 251230A/EP#01709250693 (likely EP251230a): FTW optical and NIR observations
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43258 SUBJECT: GRB 251230A/EP#01709250693 (likely EP251230a): FTW optical and NIR observations DATE: 25/12/30 02:22:30 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Xander J. Hall (CMU), Brendan O'Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report: We observed the counterpart of Swift GRB 251230A (Lanava et al. GCN 43252, Li et al. GCN 43255) which is spacially and temporally consistent with EP trigger 01709250693 (likely EP251230a) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J-band simultaneously for 2 x 180 s starting at 2025-12-30T01:50:41 UT (28.3 minutes after the trigger). We detect the counterpart in all bands and measure an r-band magnitude of r = 16.30 +/- 0.05 AB mag. The magnitude is calibrated against the PS1 catalog and not corrected for Galactic extinction. We thank Christoph Ries from the Wendelstein Observatory for the rapid response in obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/43258. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41348] LIGO/Virgo/KAGRA S251112cm: Candidates from the Vera C. Rubin Observatory
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43257 SUBJECT: LIGO/Virgo/KAGRA S251112cm: Candidates from the Vera C. Rubin Observatory DATE: 25/12/30 02:12:49 GMT FROM: Shreya Anand <shreyasahasram08(a)gmail.com> Shreya Anand (Stanford), Sean MacBride (University of Zürich), Michael Wood-Vasey (University of Pittsburgh), Erin Howard, Eric Bellm (University of Washington), Bob Armstrong (Lawrence Livermore National Laboratory), Igor Andreoni (UNC Chapel Hill), Antonella Palmese (Carnegie Mellon), Federica Bianco (University of Delaware), Tiago Ribeiro, Lynne Jones, Alysha Shugart, Narayan Khadka, Kshitija Kelkar, Danica Zilkova, Kevin Fanning, Paulina Venegas, Kate Napier, Erik Dennihy, Anastasia Alexov, Bob Blum (NSF/DOE Rubin Observatory), Robert Lupton (Princeton), Keith Bechtol (University of Wisconsin-Madison) reporting on behalf of the NSF-DOE Vera C. Rubin Observatory: We observed the localization region of the sub-solar mass merger candidate S251112cm, reported by LIGO/Virgo/KAGRA (GCN 42650, GCN 42690) with the 9.6 square degree field of view LSST Camera mounted on the 8.4-m Simonyi Survey Telescope at the Vera C. Rubin Observatory. Rubin Observatory is in an early operations period of continued system optimization, prior to beginning sustained LSST observations [1]. During this period, data quality and acquisition rate are variable. Not all data products that will be available during the Legacy Survey of Space and Time (LSST) operations are currently available [2]. Observations were conducted through engagement of the new Rubin Target-of-Opportunity advisory board, as a sub-solar mass merger does not meet the typical alert quality criteria for Rubin Target-of-Opportunity (ToO) observation [3]. We conducted observations of the localization area in LSST g and i bands, with one 30 second visit for each band, on nights 0, 2, 4, and 6 after the start of observations. First observations began on the night of November 14, 2025. We previously reported the efficiency of ToO observations on the night of November 15 2025 in GCN Circular 42707. Subsequent ToO observations continued in the following week in accordance with the recommendation from the Rubin ToO advisory board. No observations were taken on the night of November 20th due to engineering optimization activities. We report the per-band localization coverage in area and probability, along with the median limiting magnitude achieved on each night. | Date | g-band coverage [deg2] | g-band localization probability [%] | Median g-band depth [mag] | i-band coverage [deg2] | i-band localization probability [%] | Median i-band depth [mag] | |------------------- |------------------------ |------------------------------------- |--------------------------- |------------------------ |------------------------------------- |--------------------------- | | November 14, 2025 | 849.17 | 39.23 | 24.76 | 761.27 | 36.70 | 23.72 | | November 15, 2025 | - | - | - | 96.09 | 2.96 | 23.30 | | November 16, 2025 | 849.18 | 39.23 | 24.18 | 825.23 | 38.75 | 23.25 | | November 17, 2025 | - | - | - | 28.33 | 0.66 | 23.23 | | November 18, 2025 | 777.53 | 36.63 | 24.23 | 557.58 | 21.80 | 23.54 | | November 19, 2025 | 84.06 | 2.96 | 24.39 | 279.55 | 17.36 | 23.62 | | November 21, 2025 | 849.18 | 39.23 | 24.54 | 513.98 | 18.90 | 23.66 | | November 22, 2025 | - | - | - | 340.75 | 21.41 | 23.71 | Due to the lack of prior Rubin observations in most of the imaging area, we perform image differencing against Dark Energy Camera (DECam) templates. To support the usage of DECam templates, we devised a custom image processing task to create DECam templates for use with LSSTCam observations, using coadded images from the Dark Energy Survey (DES), the DECam Local Volume Exploration (DELVE) Survey, and the Dark Energy Camera All Data Everywhere (DECADE) dataset [4, 5, 6]. Apart from the DECam template task, we utilize the standard LSST data release production pipeline to obtain difference images and photometry on difference image sources [7]. To reduce the large volume of alerts in the localization to a viable set of candidate counterparts, we apply the following candidate filtering criteria: 1) exclude negative and dipole subtractions, 2) require at least 3 detections, 3) require detections in multiple filters, 4) require detections across multiple nights. Furthermore, we crossmatch against the WISE All-sky catalog [8], and exclude nuclear (within 3” of the galaxy nucleus) objects whose hosts have WISE colors consistent with active galactic nuclei (w1-w2 < -0.2 and w1-w2 > 0.65 or w2-w3 > 4.5), as well as the Million Quasars (Milliquas) AGN catalog [9] to reject likely AGN. We crossmatch against the Gaia DR3 catalog [10] and filter out likely stellar objects with reliable Gaia parallax measurements (e_Plx < 1.0). We further downselect for 1) all fading candidates, 2) all crossmatched to within a projected distance of 50 kpc of NED galaxies within the GW volume (GCN 42693), and 3) all fast rising candidates (< -0.3 mag/day), similar to young supernovae. For candidates falling into any of these categories, we visually inspect their cutouts and exclude any object that appears to be consistent with an artifact or star. We display the coordinates and lightcurve properties of the remaining candidates passing visual checks in the table below. We crossmatched the candidates to Legacy Survey Data Release 9 galaxies [11] with a crossmatch radius of 5 kpc / 12" at the GW distance. In the tables below, we note the photometric redshift of the crossmatched host galaxy for galaxy matches with photoz_err < 0.1 and mag_z < 21 mag. |tnsName|ra|dec|mjd_g|g|unc_g|mjd_i|i|unc_i|photoz|notes| |-------|--|---|-----|-|-----|-----|-|-----|------|-----| |AT2025aill|38.7231|-57.9901|60994.10|23.88|0.09|60994.16|22.12|0.05|-|transient-like (c)| |AT2025aimp|35.2965|-52.4648|60994.10|22.55|0.03|60994.16|21.58|0.03|-|transient-like (b)| |AT2025aild|30.4926|-49.3871|60994.09|23.05|0.04|60994.16|21.84|0.04|-|transient-like (c)| |AT2024aeuy|4.5991|-44.9641|60994.06|22.47|0.05|60994.14|21.05|0.02|0.163|transient-like (c,d)| |AT2025aimx|6.9966|-45.6209|60994.07|22.23|0.05|60994.14|21.59|0.04|0.294|transient-like (c)| |AT2025aimi|5.0418|-43.5832|60994.06|22.03|0.03|60994.14|21.15|0.02|0.179|transient-like (c)| |AT2025adil|4.9861|-42.849|60994.06|20.26|0.01|61001.14|20.51|0.02|0.145|transient-like (b,d)| |AT2025aimj|13.1101|-40.5702|60994.09|22.24|0.03|60994.15|22.18|0.05|0.130|transient-like; nuclear (a,b)| |AT2025aims|14.8886|-41.2259|60994.09|21.11|0.01|60994.15|20.99|0.02|-|transient-like (c)| |AT2025aile|6.4582|-39.459|60994.08|23.58|0.07|60994.14|21.96|0.04|0.220|transient-like (c)| |AT2025adkm|7.7313|-39.6507|60994.06|22.53|0.07|60994.14|20.52|0.01|0.090|transient-like (c,d)| |AT2025ailh|11.1327|-37.4762|60996.11|21.03|0.01|60994.15|20.78|0.01|0.251|transient-like (b)| |AT2025aili|352.8751|-25.2769|60994.12|22.94|0.05|60994.18|21.88|0.06|-|transient-like (c)| |AT2025aimo|350.4845|-21.584|60994.12|22.87|0.04|60999.11|22.69|0.09|-|transient-like (c)| |AT2025ailo|352.6156|-21.3053|60994.12|23.33|0.06|60994.18|22.47|0.09|-|transient-like (c)| |AT2025aimm|351.7215|-21.3579|60994.12|22.97|0.05|60994.18|22.53|0.09|-|transient-like (b)| |AT2025xhb|352.3902|-20.988|60994.12|22.51|0.04|60994.18|21.35|0.03|-|transient-like (c,d)| |AT2025aazc|351.2951|-21.0291|60994.12|20.0|0.01|60994.18|19.45|0.01|-|transient-like (c,d)| |AT2025aimr|342.8701|-14.1804|60994.11|21.39|0.02|60994.17|21.23|0.04|-|transient-like; variable? (c)| |AT2025vof|352.0114|-13.6978|60994.12|22.72|0.04|60994.18|22.06|0.06|0.111|transient-like (c,d)| |AT2025admd|345.8632|-11.0341|60996.09|20.18|0.01|60999.1|20.32|0.01|-|transient-like (c,d)| |AT2025aimn|349.9407|-11.7227|60994.12|21.58|0.02|60994.17|21.07|0.03|0.098|transient-like (b)| |AT2025adqf|344.8881|-9.4662|60994.11|21.87|0.02|60994.17|21.42|0.05|0.211|transient-like (b,d)| |AT2025wjk|342.422|-8.891|60994.11|23.26|0.1|60994.17|21.54|0.05|-|transient-like (a,b,d)| |AT2025adqe|342.2308|-0.6142|60994.11|22.48|0.04|60999.1|22.16|0.06|0.273|transient-like (b,d)| |AT2025ailp|36.1916|-55.4659|60998.15|22.86|0.07|60994.16|21.44|0.03|0.166|nuclear; transient-like (b)| |AT2025aimq|33.1928|-54.7575|60994.09|21.45|0.01|60994.16|21.26|0.02|0.216|nuclear; transient-like (c)| |AT2025adin|31.0235|-51.6365|60994.09|20.26|0.01|60996.14|20.45|0.02|0.019*|transient-like (b,d)| |AT2025aimy|358.9653|-29.1393|60994.13|22.37|0.02|60994.18|21.8|0.04|0.032*|transient-like (b)| |AT2025ailr|354.3794|-21.466|60994.13|22.3|0.03|60996.17|21.86|0.08|-|nuclear (c)| |AT2025ailz|349.9446|-18.2149|60994.12|22.78|0.04|60996.17|21.67|0.06|-|nuclear (c)| |AT2025aima|352.0986|-18.2493|60994.12|21.57|0.02|60994.18|21.19|0.03|-|nuclear (c)| |AT2025abwx|343.111|-14.6323|60994.11|19.96|0.01|60994.17|19.66|0.01|-|nuclear (c)| |AT2025ailt|342.219|-8.3411|60999.06|20.52|0.01|61001.17|20.06|0.02|0.226|nuclear (b)| |AT2025aime|341.6254|-7.0032|60994.11|22.98|0.07|60999.1|21.37|0.03|0.233|nuclear (c)| |AT2025mii|339.6744|0.2168|60994.11|21.52|0.02|60996.15|20.98|0.04|0.202|nuclear (c,d)| |AT2025aimz|357.3972|-28.2219|60994.13|23.55|0.07|60994.18|22.55|0.09|-|nuclear (a)| |AT2025aina|347.8744|-23.2679|60994.11|21.02|0.01|60994.18|21.33|0.03|-|nuclear (c)| |AT2025vyp|12.8853|-46.7011|60994.07|22.94|0.09|60994.15|20.87|0.02|-|transient-like (b,d)| |AT2025aimh|13.7904|-45.917|60994.09|23.39|0.06|60994.15|22.5|0.06|-|transient-like (a,b)| |AT2025aimg|10.5375|-41.0175|60994.07|22.54|0.07|60994.15|22.05|0.04|-|transient-like (c)| |AT2025ailv|348.1483|-10.4695|60994.12|22.65|0.04|60994.17|21.89|0.06|0.297|transient-like, nuclear (b)| |AT2025aimf|349.1835|-9.0462|60996.10|22.5|0.05|60999.11|22.4|0.07|-|transient-like (c)| |AT2025aimd|341.7576|-5.2462|60994.11|22.26|0.03|60994.17|22.35|0.11|-|transient-like (c)| |AT2025aily|1.4555|-34.251|60994.13|23.11|0.05|60994.14|22.15|0.05|-|transient-like (c)| |AT2025aimb|36.6153|-52.9123|60994.09|22.79|0.04|60994.16|22.31|0.06|-|nuclear (a,b)| |AT2025ailn|13.1636|-45.0198|60994.09|22.84|0.04|60994.15|22.43|0.06|-|nuclear (a,b)| |AT2025ailk|13.4689|-41.8303|60994.09|21.97|0.02|60998.19|21.57|0.05|-|nuclear (c)| |AT2025aimt|13.6167|-39.7345|60994.09|23.13|0.05|60994.15|22.39|0.06|-|nuclear (c)| |AT2025ailq|4.7717|-34.3991|60994.13|21.9|0.02|60994.14|21.98|0.05|-|nuclear (c)| |AT2025aimc|350.1702|-12.5501|60994.12|23.07|0.08|60999.11|22.44|0.08|-|star offset from galaxy? (c)| |AT2025aimu|349.0499|-11.0721|60994.12|23.62|0.09|60994.17|21.91|0.06|0.264|transient-like (a,b)| |AT2025aimk|338.775|-3.2786|60994.11|22.33|0.03|60996.15|21.83|0.08|0.269|nuclear; transient-like (c)| *Spectroscopic redshifts from the NED-GWF. These two transients are within 50 kpc of a NED galaxy within the GW localization volume. We note, however, that both of these transients are also closely offset from another galaxy with no crossmatch to the Legacy Survey DR8 catalog. (a) These candidates exhibit some rising behavior in their lightcurves in at least one band. (b) These candidates are fading by >0.1 mag/day in at least one band. (c) These candidates exhibit very slow or nearly flat evolution in both bands. (d) These candidates were previously reported by another survey. In the table above, we recover the following previously reported candidates: AT2024aeuy (GOTO), AT2025adil (GOTO, ATLAS), AT2025adkm (GW-MMADS), AT2025aazc (ZTF, GOTO, ATLAS, GW-MMADS), AT2025admd (GW-MMADS, GOTO), AT2025adqf (GW-MMADS), AT2025adqe (GW-MMADS, WFST), AT2025vof (ZTF, ATLAS, GOTO, PS1), AT2025xhb (ALeRCE, ATLAS), AT2025wjk (PS1), AT2025adin (GOTO), AT2025abwx (GOTO, ZTF, ATLAS), AT2025mii (YSE, GOTO, PS1, GW-MMADS), AT2025vyp (ATLAS). AT2024aeuy, AT2025aazc, AT2025vof, AT2025xhb, AT2025wjk, AT2025mii, and AT2025vyp were discovered over a month prior to the GW merger time, and hence are unlikely to be associated with S251112cm. From our table, we highlight the following candidates that exhibit fast-fading (~0.2 mag/day) behavior in at least one band: AT2025aimp, AT2025aimn and AT2025adqf. We also note that AT2025adin and AT2025aimy (both within 50 kpc of a NED-GWF galaxy) exhibit fading in both g- and i-bands. We also highlight the following candidates that show rising behavior and could therefore be consistent with young supernovae (though we lack non-detections to constrain age): AT2025aimj, AT2025aimz, AT2025aimb, AT2025ailn, AT2025aimu. For completeness, we also report the following candidates found in our search that have photometric redshifts from Legacy Survey that are inconsistent with the GW localization volume (photo-z > 0.3): |tnsName|ra|dec|mjd_g|g|unc_g|mjd_i|i|unc_i|photoz|notes| |-------|--|---|-----|-|-----|-----|-|-----|------|--------| |AT2025ailu|349.9378|-11.0639|60994.12|23.2|0.07|60994.17|21.93|0.06|0.31|transient-like (c)| |AT2025ailm|33.0616|-54.6792|60994.09|23.46|0.06|60994.16|22.4|0.06|0.464|transient-like (c)| |AT2025ailc|33.8628|-49.8144|60994.09|22.12|0.02|60994.16|22.01|0.04|0.367|transient-like (b)| |AT2025ails|1.8871|-35.6877|60994.13|22.9|0.04|60994.14|22.36|0.07|0.413|transient-like; nuclear (a,b)| |AT2025ailj|5.0313|-35.5348|60994.13|22.18|0.03|60994.14|21.83|0.04|0.301|transient-like (c)| |AT2025aimv|349.8256|-11.5522|60994.12|23.44|0.08|60994.17|22.24|0.07|0.422|transient-like (c)| |AT2025aimw|338.0421|-6.4624|60994.11|21.82|0.02|60999.1|21.61|0.06|0.31|transient-like (c)| |AT2025ailw|341.7785|-5.2592|60994.11|22.68|0.04|60994.17|22.17|0.09|0.353|transient-like, nuclear (b)| |AT2025adjw|33.5605|-54.15|60994.09|21.82|0.02|60994.16|21.56|0.03|0.313|nuclear (a,d)| |AT2025aiki|3.9504|-42.2778|60994.06|21.98|0.03|60994.14|21.68|0.04|0.364|nuclear (c)| |AT2025aiml|4.8617|-35.0092|60994.13|21.31|0.01|60994.14|21.67|0.04|1.039|nuclear (c)| |AT2025ailg|340.7488|-1.6196|60994.11|21.99|0.03|60996.15|21.78|0.08|0.921|stellar/nuclear (c)| |AT2025ailf|11.8653|-44.0097|60994.07|22.43|0.07|60994.15|22.3|0.06|0.417|nuclear (a)| |AT2025ailx|345.1107|-9.1446|60994.11|22.23|0.03|60994.17|21.47|0.05|0.481|nuclear (c)| In addition to the DECam-Rubin processing, we also perform image subtraction with custom Rubin templates dynamically built during the observing campaign. As the flux of detected transients will be present in the templates, we use this stream mainly as an additional verification of candidates identified from the DECam-Rubin stream. We note that the following candidates are recovered independently by both streams: AT2025aild, AT2024aeuy, AT2025adkm, AT2025aimm, AT2025aimr, AT2025aimn, AT2025ailu, AT2025adqf, AT2025adqe, AT2025aima, AT2025vyp, AT2025aimh, AT2025ailj, AT2025ailv, AT2025aimw, AT2025ailw, AT2025aimb, AT2025ailk, AT2025aiml, AT2025aimc, and AT2025ailx. We encourage further follow-up to discern the nature of the candidates reported above. We thank all who contributed to the design and implementation of the Vera C. Rubin Observatory Target-of-Opportunity system, including but not limited to, the LSST Transients and Variable Stars Science Collaboration Multiwavelength Characterization and Counterparts subgroup. We especially thank the Rubin Observatory observers, who are instrumental to the performance and success of the LSST. This material is based upon work supported in part by the National Science Foundation through Cooperative Agreements AST-1258333 and AST-2241526 and Cooperative Support Agreements AST-1202910 and 2211468 managed by the Association of Universities for Research in Astronomy (AURA), and the Department of Energy under Contract No. DE-AC02-76SF00515 with the SLAC National Accelerator Laboratory managed by Stanford University. Additional Rubin Observatory funding comes from private donations, grants to universities, and in-kind support from LSST-DA Institutional Members. [1] sitcomtn-005.lsst.io, §6 [2] lse-163.lsst.io [3] Rubin ToO 2024: Envisioning the Vera C. Rubin Observatory LSST Target of Opportunity program, Andreoni et al. (2024) [4] The Dark Energy Survey Data Release 2, DES Collaboration et al. (2021) [5] The DECam Local Volume Exploration Survey Data Release 2, Drlica-Wagner et al. (2022) [6] The DECADE cosmic shear project I: A new weak lensing shape catalog of 107 million galaxies, Anbajagane et al. (2025) [7] pstn-019.lsst.io [8] VizieR On-line Data Catalog: II/328, Cutri et al. (2013) [9] VizieR On-line Data Catalog: VII/294, Flesch et al. (2023) [10] VizieR On-line Data Catalog: I/355, Gaia Collaboration (2022) [11] Overview of the DESI Legacy Imaging Surveys, DESI Collaboration, Dey et al. (2019) View this GCN Circular online at https://gcn.nasa.gov/circulars/43257. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41347] Swift GRB 251230A: Global MASTER-Net observations report
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43256 SUBJECT: Swift GRB 251230A: Global MASTER-Net observations report DATE: 25/12/30 02:03:04 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-SAAO robotic telescope [1] located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 251230A ( S. Lanava et al., GCN 43252) errorbox 1907 sec after notice time and 1930 sec after trigger time at 2025-12-30 01:53:52 UT, with upper limit up to 19.7 mag. The observations began at zenith distance = 53 deg. The sun altitude is -18.1 deg. The galactic latitude b = 70 deg., longitude l = 265 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3090261 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 2021 | MASTER-SAAO | C | 180 | 19.7 | 2021 | MASTER-SAAO | C | 180 | 14.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43256. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41346] The EP-WXT trigger 01709250693/GRB 251230a: Las Cumbres detection of the optical counterpart
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43255 SUBJECT: The EP-WXT trigger 01709250693/GRB 251230a: Las Cumbres detection of the optical counterpart DATE: 25/12/30 02:02:19 GMT FROM: Wenxiong Li at NAOC <liwenxiong1992(a)gmail.com> Wenxiong Li, Runduo Liang (NAOC), Iair Arcavi (TAU), Ido Keinan (TAU), David Sand (U of Arizona) We observed the position of EP-WXT trigger 01709250693/GRB 251230a with a Las Cumbres 1m telescope at Sutherland Observatory, South Africa, 9 mins after the Einstein Probe WXT trigger. We took 2x300s exposures in the broad optical w band. We find an uncataloged source at RA=179.8972, Dec=11.4383 within the EP-WXT error circle and measure the following preliminary photometry calibrated to the r band: MJD 61039.063 Mag 15.1 The position of the counterpart is consistent with that reported by Lanava et al. (GCN 43252). View this GCN Circular online at https://gcn.nasa.gov/circulars/43255. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41345] EP251229a: Global MASTER-Net observations report
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43254 SUBJECT: EP251229a: Global MASTER-Net observations report DATE: 25/12/30 01:54:26 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Tunka robotic telescope [1] located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the EP251229a ( EP Team et al., GCN 43253) errorbox 635 sec after trigger time at 2025-12-29 20:09:24 UT, with upper limit up to 15.9 mag. The observations began at zenith distance = 19 deg. The sun altitude is -45.6 deg. The galactic latitude b = 33 deg., longitude l = 185 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3090301 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 665 | 2025-12-29 20:09:24 | MASTER-Tunka | (08h 15m 31.75s , +37d 38m 46.9s) | P- | 60 | 15.1 | 665 | 2025-12-29 20:09:24 | MASTER-Tunka | (08h 14m 38.46s , +37d 47m 55.5s) | P| | 60 | 14.4 | 729 | 2025-12-29 20:10:27 | MASTER-Tunka | (08h 15m 31.53s , +37d 38m 43.3s) | P- | 60 | 15.7 | 729 | 2025-12-29 20:10:27 | MASTER-Tunka | (08h 14m 38.47s , +37d 47m 47.0s) | P| | 60 | 13.9 | 792 | 2025-12-29 20:11:31 | MASTER-Tunka | (08h 15m 31.64s , +37d 38m 42.0s) | P- | 60 | 15.7 | 792 | 2025-12-29 20:11:31 | MASTER-Tunka | (08h 14m 38.68s , +37d 47m 50.3s) | P| | 60 | 14.4 | 856 | 2025-12-29 20:12:34 | MASTER-Tunka | (08h 15m 31.62s , +37d 38m 39.6s) | P- | 60 | 15.7 | 856 | 2025-12-29 20:12:34 | MASTER-Tunka | (08h 14m 42.54s , +37d 48m 11.2s) | P| | 60 | 11.9 | 919 | 2025-12-29 20:13:38 | MASTER-Tunka | (08h 14m 38.71s , +37d 47m 49.4s) | P| | 60 | 14.4 | 919 | 2025-12-29 20:13:38 | MASTER-Tunka | (08h 15m 31.64s , +37d 38m 37.7s) | P- | 60 | 15.7 | 983 | 2025-12-29 20:14:41 | MASTER-Tunka | (08h 15m 31.63s , +37d 38m 36.0s) | P- | 60 | 15.7 | 983 | 2025-12-29 20:14:41 | MASTER-Tunka | (08h 14m 38.72s , +37d 47m 38.4s) | P| | 60 | 14.0 | 1050 | 2025-12-29 20:15:49 | MASTER-Tunka | (08h 15m 31.60s , +37d 38m 34.3s) | P- | 60 | 15.7 | 1050 | 2025-12-29 20:15:49 | MASTER-Tunka | (08h 14m 38.88s , +37d 47m 44.8s) | P| | 60 | 14.4 | 1114 | 2025-12-29 20:16:52 | MASTER-Tunka | (08h 15m 31.84s , +37d 38m 36.2s) | P- | 60 | 15.0 | 1114 | 2025-12-29 20:16:52 | MASTER-Tunka | (08h 14m 38.84s , +37d 47m 29.7s) | P| | 60 | 14.0 | 1177 | 2025-12-29 20:17:56 | MASTER-Tunka | (08h 15m 31.72s , +37d 38m 31.1s) | P- | 60 | 15.9 | 1177 | 2025-12-29 20:17:56 | MASTER-Tunka | (08h 14m 38.85s , +37d 47m 27.3s) | P| | 60 | 14.0 | 1240 | 2025-12-29 20:18:59 | MASTER-Tunka | (08h 14m 39.62s , +37d 47m 47.2s) | P| | 60 | 14.3 | 1240 | 2025-12-29 20:18:59 | MASTER-Tunka | (08h 15m 32.02s , +37d 38m 31.4s) | P- | 60 | 15.2 | 1304 | 2025-12-29 20:20:02 | MASTER-Tunka | (08h 15m 31.81s , +37d 38m 27.8s) | P- | 60 | 15.9 | 1367 | 2025-12-29 20:21:06 | MASTER-Tunka | (08h 15m 32.10s , +37d 38m 28.0s) | P- | 60 | 15.4 | 1367 | 2025-12-29 20:21:06 | MASTER-Tunka | (08h 14m 39.08s , +37d 47m 30.2s) | P| | 60 | 14.6 | 1431 | 2025-12-29 20:22:09 | MASTER-Tunka | (08h 14m 38.88s , +37d 47m 07.2s) | P| | 60 | 14.4 | 1431 | 2025-12-29 20:22:09 | MASTER-Tunka | (08h 15m 31.88s , +37d 38m 24.7s) | P- | 60 | 15.7 | 1494 | 2025-12-29 20:23:13 | MASTER-Tunka | (08h 15m 32.16s , +37d 38m 24.7s) | P- | 60 | 15.1 | 1494 | 2025-12-29 20:23:13 | MASTER-Tunka | (08h 14m 39.04s , +37d 47m 20.0s) | P| | 60 | 13.9 | 1558 | 2025-12-29 20:24:16 | MASTER-Tunka | (08h 15m 32.26s , +37d 38m 21.8s) | P- | 60 | 15.3 | The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43254. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41344] EP251229a: Einstein Probe detection of an X-ray transient
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43253 SUBJECT: EP251229a: Einstein Probe detection of an X-ray transient DATE: 25/12/30 01:49:26 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> B. T. Wang (YNAO, CAS), J. P. Chen (SYSU), D. Zhu, K. J. Zhang (YNU), Y. L. Wang (NAO, CAS; ICE, CSIC-IEEC) and Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP251229a. The transient triggered EP-WXT (ID: 01709250690) at 2025-12-29T19:58:49 (UTC). The WXT position of the source is R.A. =124.103 deg, DEC = 37.224 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 124.1057 deg, DEC = 37.2073 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data are received. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/43253. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41343] EP251229a: Einstein Probe detection of an X-ray transient
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43253 SUBJECT: EP251229a: Einstein Probe detection of an X-ray transient DATE: 25/12/30 01:49:26 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> B. T. Wang (YNAO, CAS), J. P. Chen (SYSU), D. Zhu, K. J. Zhang (YNU), Y. L. Wang (NAO, CAS; ICE, CSIC-IEEC) and Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP251229a. The transient triggered EP-WXT (ID: 01709250690) at 2025-12-29T19:58:49 (UTC). The WXT position of the source is R.A. =124.103 deg, DEC = 37.224 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 124.1057 deg, DEC = 37.2073 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data are received. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/43253. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41342] GRB 251230A: Swift detection of a burst with a bright optical counterpart
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43252 SUBJECT: GRB 251230A: Swift detection of a burst with a bright optical counterpart DATE: 25/12/30 01:48:56 GMT FROM: Simone Dichiara at Pennsylvania State University <sbd5667(a)psu.edu> S. Lanava (PSU), S. Dichiara (PSU) and R. Gupta (NASA GSFC) report on behalf of the Neil Gehrels Swift Observatory Team: At 01:21:41 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251230A (trigger=1429020). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 179.894, +11.415 which is RA(J2000) = 11h 59m 35s Dec(J2000) = +11d 24' 55" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multiple-peaked structure with a duration of about 80 sec. The peak count rate was ~5000 counts/sec (15-350 keV), at ~30 sec after the trigger. The XRT began observing the field at 01:22:49.3 UT, 68.1 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source with an enhanced position: RA, Dec 179.89781, 11.43828 which is equivalent to: RA(J2000) = 11h 59m 35.47s Dec(J2000) = +11d 26' 17.8" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 84 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (1.88 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.4 (+1.47/-1.34) x 10^21 cm^-2 (90% confidence). The initial flux in the 2.5 s image was 4.73e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 76 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 11:59:35.42 = 179.89760 DEC(J2000) = +11:26:19.3 = 11.43870 with a 90%-confidence error radius of about 0.74 arc sec. This position is 4.7 arc sec. from the center of the XRT error circle. The estimated magnitude is 13.74 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.024. Burst Advocate for this burst is S. Lanava (sml7284 AT psu.edu) Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/43252. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41341] GRB 251226A: Glowbug gamma-ray detection
by GCN Circulars 29 Dec '25

29 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43251 SUBJECT: GRB 251226A: Glowbug gamma-ray detection DATE: 25/12/29 14:51:57 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 251226A, which was also detected by GECAM-B, SVOM/GRM, and HXMT (GCN 43244, 43245). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-12-26 08:01:02.528 with a duration of 9.2 s and a total significance of about 15.9 sigma. The light curve comprises a single peak corresponding to the initial brightest peak seen in the GECAM-B and SVOM/GRM light curves. The burst originated toward the Nadir side of Glowbug and was detected despite passing through the passive material from the H9 pallet and internal passive material/shielding within Glowbug. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/43251. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41340] GRB 251222A/EP251222b: 1.6m Mephisto optical followup
by GCN Circulars 29 Dec '25

29 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43250 SUBJECT: GRB 251222A/EP251222b: 1.6m Mephisto optical followup DATE: 25/12/29 11:31:46 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh(a)ynu.edu.cn> Brajesh Kumar, Shiyan Zhong, Guowang Du, Hongguang Li, Dan Zhu, Yu Pan, Yuan Fang, Xingzhu Zou, Xinlei Chen, Xufeng Zhu, Tao Wang, Jinghua Zhang, Yehao Cheng, Xinzhong Er, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team: We observed GRB 251222A/EP251222b (SVOM burst-id sb25122206, Yang et al. GCN 43188; Fermi/GBM, GCN 43186; EP-WXT, Guo et al., GCN 43201) with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at the Lijiang Observatory. Multi-band (ugi and vrz) simultaneous observations were acquired in two sets using the newly installed three mosaic cameras. The first set (in ugi bands) and the second set (in vrz and ugi bands) of observations were started from 17:11:08T2025-12-22 (~5 min after the SVOM trigger) and 17:48:08T2025-12-22, respectively. These observations were continued till 2025-12-22T19:23:19. The optical counterpart reported previously (Palmerio et al., GCN 43189; An et. al, GCN 43194; Calapai et. al, GCN 43195; Durbak et. al, GCN 43197; Li et. al, GCN 43203; Saccardi et. al, GCN 43208; Gupta et. al, GCN 43207 GCN 43224; Saccardi et. al, GCN 43204; Kumar et. al, GCN 43209; Pérez-Fournon et. al, GCN 43212; Globus et al., GCN 43225; Pankov et al., GCN 43226; Freeberg et al., GCN 43229; Volnova et al., GCN 43230; Busmann et al., GCN 43233; Lee et al., GCN 43236; Maksut et al., GCN 43237) was clearly detected in our vgriz bands but not in u band. Although our first set of observations is limited, the overall preliminary light curves indicate a decay trend during ~300 - 2500 sec and a rise afterward. The preliminary photometric magnitudes of initial frames are listed below. These magnitudes are not corrected for the Galactic extinction in the direction of the burst. ------------------------------------------------------------------ Start_Time(UT) |Band | Exp(s)| Mag/LimMag (AB) ---------------------|------|-------|----------------------------- 2025-12-22T17:11:08 | u | 45*2 | >20.85 2025-12-22T17:48:08 | v | 60*3 | 21.41 +/- 0.32 2025-12-22T17:11:11 | g | 45 | 18.28 +/- 0.05 2025-12-22T17:48:10 | r | 60 | 19.18 +/- 0.08 2025-12-22T17:11:11 | i | 45 | 17.60 +/- 0.03 2025-12-22T17:48:10 | z | 60 | 19.02 +/- 0.23 ------------------------------------------------------------------ Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. The facility is operated by the South-Western Institute for Astronomy Research (SWIFAR), Yunnan University. It provides real-time, high-quality colors of stellar objects. The Mephisto mosaic cameras were installed in October 2025. The first light was achieved in all three channels on 10 October 2025, and presently, these are under the commissioning phase. All the data have been reduced by the Mephisto data processing pipeline. Here, we note that the current data processing pipeline is still at a preliminary stage, with flux calibration precision in each band at the level of about 5% or even higher. ------------------------------------------------------------------- View this GCN Circular online at https://gcn.nasa.gov/circulars/43250. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41339] GRB 251129A: redshift correction and SN detection at z = 0.505 with GTC
by GCN Circulars 28 Dec '25

28 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43249 SUBJECT: GRB 251129A: redshift correction and SN detection at z = 0.505 with GTC DATE: 25/12/28 16:36:39 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> A. de Ugarte Postigo (LAM), A. Martin-Carrillo (UCD), L. Izzo (INAF/OACN and DARK/NBI), B. Schneider (LAM), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), C. C. Thoene (AbAO), N. R. Tanvir (Univ. Leicester), J. F. Agui Fernandez (CAHA), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), S. Geier (GTC), G. Lombardi (GTC), N. A. Rakotondrainibe (LAM), A. Cabrera-Lavers (GTC), report: We have continued monitoring the optical counterpart (Angulo et al. GCN 42880) of GRB 251129A (Wenjun et al. GCN 42877) using the 10.4 m Gran Telescopio Canarias (GTC) equipped with OSIRIS+ and HiPERCAM. We observed the afterglow in imaging using the u, g, r, i, z bands on 8 December 2025 (9.2 day after the burst) and again on 26 December 2025 (27.2 day after the burst). The optical counterpart is well detected in both epochs, with an increase in brightness in all bands. At 27.2 days after the burst, we measure r = 22.24 +/- 0.04 mag. The object is significantly brighter than the candidate host underlying the GRB, which we measure at r ~ 24.16 mag in CFHT archival images. On 27 December 2025, 28.1 days after the burst, we obtained a 3x1200 s spectrum using OSIRIS+ equipped with grism R1000B, covering the range between 3700 and 7780 AA at a resolving power of ~600. The spectrum shows a continuum over the full spectral range. We do not detect any of the spectral features reported by Sánchez-Ramírez et al. (GCN 42900) at z = 1.460. However, we detect emission features of [OII], [OIII], H-alpha, H-beta and H-gamma from an underlying galaxy at a common redshift of z = 0.505. At a redshift of z = 0.505, the emergence of a detectable SN is expected, which explains the rebrightening observed in our photometric data. Hence, we suggest that the redshift of GRB 251129A is indeed z = 0.505 and that we are now observing the associated SN. We do note that the observed emission is brighter than what we would expect for a template of SN 1998bw at z = 0.505, even after correction of host galaxy contribution, although our photometry may be affected by the remaining light of the afterglow. We encourage further follow-up of this event. This work has used the GRBspec database at http://grbspec.eu (de Ugarte Postigo et al. 2014, doi:10.1117/12.2055774). View this GCN Circular online at https://gcn.nasa.gov/circulars/43249. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41338] Fermi GRB 251228A: Global MASTER-Net observations report
by GCN Circulars 28 Dec '25

28 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43248 SUBJECT: Fermi GRB 251228A: Global MASTER-Net observations report DATE: 25/12/28 05:15:35 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 251228A ( Fermi GBM team, GCN 43246) errorbox 4566 sec after notice time and 4601 sec after trigger time at 2025-12-28 01:58:51 UT, with upper limit up to 17.7 mag. The observations began at zenith distance = 14 deg. The sun altitude is -28.7 deg. The galactic latitude b = 51 deg., longitude l = 166 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3087807 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 4631 | 2025-12-28 01:58:51 | MASTER-Kislovodsk | (10h 04m 18.19s , +50d 46m 44.1s) | C | 60 | 17.2 | 4631 | 2025-12-28 01:58:51 | MASTER-Kislovodsk | (09h 57m 14.55s , +51d 07m 25.1s) | C | 60 | 17.5 | 4723 | 2025-12-28 02:00:23 | MASTER-Kislovodsk | (09h 59m 11.64s , +48d 50m 59.9s) | C | 60 | 17.0 | 4725 | 2025-12-28 02:00:25 | MASTER-Kislovodsk | (09h 52m 24.48s , +49d 12m 11.6s) | C | 60 | 17.4 | 4829 | 2025-12-28 02:02:09 | MASTER-Kislovodsk | (09h 45m 17.93s , +50d 44m 48.3s) | C | 60 | 17.2 | 4829 | 2025-12-28 02:02:09 | MASTER-Kislovodsk | (09h 38m 14.89s , +51d 05m 43.5s) | C | 60 | 17.3 | 4922 | 2025-12-28 02:03:42 | MASTER-Kislovodsk | (10h 17m 30.25s , +48d 53m 01.1s) | C | 60 | 17.0 | 4922 | 2025-12-28 02:03:42 | MASTER-Kislovodsk | (10h 10m 42.22s , +49d 14m 15.0s) | C | 60 | 17.4 | 5018 | 2025-12-28 02:05:17 | MASTER-Kislovodsk | (09h 50m 33.43s , +52d 39m 46.6s) | C | 60 | 17.1 | 5018 | 2025-12-28 02:05:18 | MASTER-Kislovodsk | (09h 43m 11.63s , +53d 00m 12.0s) | C | 60 | 17.3 | 5337 | 2025-12-28 02:10:37 | MASTER-Kislovodsk | (10h 04m 06.83s , +50d 46m 06.6s) | C | 60 | 17.5 | 5337 | 2025-12-28 02:10:37 | MASTER-Kislovodsk | (09h 57m 01.40s , +51d 05m 30.2s) | C | 60 | 17.3 | 5429 | 2025-12-28 02:12:08 | MASTER-Kislovodsk | (09h 59m 08.41s , +48d 52m 46.4s) | C | 60 | 17.7 | 5429 | 2025-12-28 02:12:08 | MASTER-Kislovodsk | (09h 52m 19.73s , +49d 12m 21.2s) | C | 60 | 17.3 | 5523 | 2025-12-28 02:13:43 | MASTER-Kislovodsk | (09h 45m 15.46s , +50d 45m 29.2s) | C | 60 | 17.3 | 5523 | 2025-12-28 02:13:43 | MASTER-Kislovodsk | (09h 38m 11.21s , +51d 04m 53.5s) | C | 60 | 17.0 | 5619 | 2025-12-28 02:15:19 | MASTER-Kislovodsk | (10h 17m 21.80s , +48d 51m 08.9s) | C | 60 | 17.3 | 5619 | 2025-12-28 02:15:19 | MASTER-Kislovodsk | (10h 10m 32.65s , +49d 10m 46.8s) | C | 60 | 17.3 | 5717 | 2025-12-28 02:16:57 | MASTER-Kislovodsk | (09h 50m 31.71s , +52d 39m 11.2s) | C | 60 | 17.5 | 5717 | 2025-12-28 02:16:57 | MASTER-Kislovodsk | (09h 43m 09.29s , +52d 58m 26.3s) | C | 60 | 17.0 | 5816 | 2025-12-28 02:18:36 | MASTER-Kislovodsk | (10h 10m 16.22s , +52d 41m 00.0s) | C | 60 | 17.4 | 5816 | 2025-12-28 02:18:36 | MASTER-Kislovodsk | (10h 02m 52.62s , +53d 00m 22.2s) | C | 60 | 17.1 | 5914 | 2025-12-28 02:20:14 | MASTER-Kislovodsk | (09h 55m 09.39s , +46d 56m 17.6s) | C | 60 | 17.2 | 5914 | 2025-12-28 02:20:14 | MASTER-Kislovodsk | (09h 48m 36.78s , +47d 16m 10.0s) | C | 60 | 17.0 | 6009 | 2025-12-28 02:21:49 | MASTER-Kislovodsk | (10h 04m 12.28s , +50d 46m 34.1s) | C | 60 | 17.4 | 6010 | 2025-12-28 02:21:50 | MASTER-Kislovodsk | (09h 57m 07.42s , +51d 06m 00.2s) | C | 60 | 17.3 | 6529 | 2025-12-28 02:30:29 | MASTER-Kislovodsk | (10h 17m 24.80s , +48d 52m 37.6s) | C | 60 | 17.1 | 6529 | 2025-12-28 02:30:29 | MASTER-Kislovodsk | (10h 10m 29.17s , +49d 12m 12.1s) | C | 60 | 17.1 | 6625 | 2025-12-28 02:32:04 | MASTER-Kislovodsk | (09h 50m 35.30s , +52d 39m 13.1s) | C | 60 | 17.1 | 6625 | 2025-12-28 02:32:04 | MASTER-Kislovodsk | (09h 43m 06.45s , +52d 58m 20.9s) | C | 60 | 17.0 | 6721 | 2025-12-28 02:33:40 | MASTER-Kislovodsk | (10h 10m 16.53s , +52d 38m 50.2s) | C | 60 | 17.4 | 6721 | 2025-12-28 02:33:41 | MASTER-Kislovodsk | (10h 02m 46.74s , +52d 58m 01.9s) | C | 60 | 16.9 | 6817 | 2025-12-28 02:35:17 | MASTER-Kislovodsk | (09h 55m 16.58s , +46d 56m 01.5s) | C | 60 | 17.0 | 6818 | 2025-12-28 02:35:17 | MASTER-Kislovodsk | (09h 48m 38.37s , +47d 15m 51.9s) | C | 60 | 17.1 | 6917 | 2025-12-28 02:36:56 | MASTER-Kislovodsk | (10h 04m 11.56s , +50d 46m 10.2s) | C | 60 | 17.6 | 6917 | 2025-12-28 02:36:56 | MASTER-Kislovodsk | (09h 57m 00.57s , +51d 05m 34.7s) | C | 60 | 17.0 | 7013 | 2025-12-28 02:38:33 | MASTER-Kislovodsk | (09h 59m 12.42s , +48d 50m 02.1s) | C | 60 | 17.6 | 7013 | 2025-12-28 02:38:33 | MASTER-Kislovodsk | (09h 52m 19.00s , +49d 09m 39.2s) | C | 60 | 17.3 | 7112 | 2025-12-28 02:40:12 | MASTER-Kislovodsk | (09h 45m 14.59s , +50d 45m 25.6s) | C | 60 | 17.3 | 7112 | 2025-12-28 02:40:12 | MASTER-Kislovodsk | (09h 38m 05.16s , +51d 04m 52.0s) | C | 60 | 17.1 | 7211 | 2025-12-28 02:41:50 | MASTER-Kislovodsk | (10h 17m 23.46s , +48d 51m 25.4s) | C | 60 | 17.0 | 7211 | 2025-12-28 02:41:50 | MASTER-Kislovodsk | (10h 10m 28.94s , +49d 11m 03.4s) | C | 60 | 17.0 | 7303 | 2025-12-28 02:43:23 | MASTER-Kislovodsk | (09h 50m 26.54s , +52d 39m 48.9s) | C | 60 | 17.1 | 7304 | 2025-12-28 02:43:23 | MASTER-Kislovodsk | (09h 42m 58.14s , +52d 59m 02.1s) | C | 60 | 16.9 | 7400 | 2025-12-28 02:45:00 | MASTER-Kislovodsk | (10h 10m 20.94s , +52d 39m 34.4s) | C | 60 | 17.4 | 7400 | 2025-12-28 02:45:00 | MASTER-Kislovodsk | (10h 02m 51.64s , +52d 58m 42.7s) | C | 60 | 17.2 | 7497 | 2025-12-28 02:46:37 | MASTER-Kislovodsk | (10h 10m 37.66s , +52d 39m 35.2s) | C | 60 | 12.4 | 7497 | 2025-12-28 02:46:37 | MASTER-Kislovodsk | (10h 03m 48.11s , +52d 58m 42.0s) | C | 60 | 12.5 | 7596 | 2025-12-28 02:48:16 | MASTER-Kislovodsk | (10h 04m 13.05s , +50d 44m 13.4s) | C | 60 | 17.4 | 7596 | 2025-12-28 02:48:16 | MASTER-Kislovodsk | (09h 57m 03.22s , +51d 03m 35.3s) | C | 60 | 17.2 | 7688 | 2025-12-28 02:49:47 | MASTER-Kislovodsk | (09h 59m 10.08s , +48d 51m 01.6s) | C | 60 | 17.5 | 7693 | 2025-12-28 02:49:53 | MASTER-Kislovodsk | (09h 52m 17.21s , +49d 10m 37.4s) | C | 60 | 17.3 | 7789 | 2025-12-28 02:51:29 | MASTER-Kislovodsk | (09h 45m 10.11s , +50d 43m 08.7s) | C | 60 | 17.4 | 7789 | 2025-12-28 02:51:29 | MASTER-Kislovodsk | (09h 38m 01.62s , +51d 02m 36.5s) | C | 60 | 17.1 | 7886 | 2025-12-28 02:53:06 | MASTER-Kislovodsk | (10h 17m 25.04s , +48d 51m 56.3s) | C | 60 | 17.3 | 7886 | 2025-12-28 02:53:06 | MASTER-Kislovodsk | (10h 10m 30.87s , +49d 11m 36.2s) | C | 60 | 17.1 | 7982 | 2025-12-28 02:54:42 | MASTER-Kislovodsk | (09h 50m 24.96s , +52d 38m 17.5s) | C | 60 | 17.5 | 7982 | 2025-12-28 02:54:42 | MASTER-Kislovodsk | (09h 42m 57.33s , +52d 57m 33.9s) | C | 60 | 17.1 | 8081 | 2025-12-28 02:56:20 | MASTER-Kislovodsk | (10h 10m 11.14s , +52d 40m 06.1s) | C | 60 | 17.4 | 8081 | 2025-12-28 02:56:20 | MASTER-Kislovodsk | (10h 02m 42.12s , +52d 59m 17.2s) | C | 60 | 17.3 | 8180 | 2025-12-28 02:57:59 | MASTER-Kislovodsk | (09h 55m 12.19s , +46d 55m 29.4s) | C | 60 | 17.2 | 8180 | 2025-12-28 02:57:59 | MASTER-Kislovodsk | (09h 48m 35.03s , +47d 15m 37.7s) | C | 60 | 17.0 | 8586 | 2025-12-28 03:04:46 | MASTER-Kislovodsk | (10h 17m 18.67s , +48d 51m 29.6s) | C | 60 | 17.1 | 8586 | 2025-12-28 03:04:46 | MASTER-Kislovodsk | (10h 10m 24.95s , +49d 11m 15.6s) | C | 60 | 17.1 | 8683 | 2025-12-28 03:06:23 | MASTER-Kislovodsk | (09h 50m 27.29s , +52d 37m 39.4s) | C | 60 | 17.1 | 8683 | 2025-12-28 03:06:23 | MASTER-Kislovodsk | (09h 43m 00.39s , +52d 57m 00.0s) | C | 60 | 17.1 | 8780 | 2025-12-28 03:08:00 | MASTER-Kislovodsk | (10h 10m 07.36s , +52d 37m 32.7s) | C | 60 | 17.4 | 8780 | 2025-12-28 03:08:00 | MASTER-Kislovodsk | (10h 02m 39.26s , +52d 56m 48.2s) | C | 60 | 17.3 | 8878 | 2025-12-28 03:09:37 | MASTER-Kislovodsk | (10h 10m 28.03s , +52d 37m 34.5s) | C | 60 | 12.6 | 8964 | 2025-12-28 03:11:03 | MASTER-Kislovodsk | (10h 12m 23.19s , +52d 37m 37.7s) | C | 60 | 12.3 | 9055 | 2025-12-28 03:12:35 | MASTER-Kislovodsk | (10h 12m 40.99s , +46d 55m 07.8s) | C | 60 | 17.4 | 9056 | 2025-12-28 03:12:35 | MASTER-Kislovodsk | (10h 06m 03.32s , +47d 15m 13.0s) | C | 60 | 17.4 | 9149 | 2025-12-28 03:14:09 | MASTER-Kislovodsk | (10h 23m 06.85s , +50d 45m 12.8s) | C | 60 | 16.9 | 9154 | 2025-12-28 03:14:14 | MASTER-Kislovodsk | (10h 15m 55.96s , +51d 04m 45.2s) | C | 60 | 17.1 | 9252 | 2025-12-28 03:15:51 | MASTER-Kislovodsk | (09h 56m 46.97s , +54d 31m 51.5s) | C | 60 | 17.1 | 9252 | 2025-12-28 03:15:52 | MASTER-Kislovodsk | (09h 48m 58.93s , +54d 50m 53.6s) | C | 60 | 17.1 | 9346 | 2025-12-28 03:17:26 | MASTER-Kislovodsk | (09h 37m 26.63s , +46d 54m 36.9s) | C | 60 | 17.2 | 9346 | 2025-12-28 03:17:26 | MASTER-Kislovodsk | (09h 30m 52.56s , +47d 15m 10.2s) | C | 60 | 17.2 | 9444 | 2025-12-28 03:19:04 | MASTER-Kislovodsk | (10h 10m 12.18s , +52d 38m 01.4s) | C | 60 | 17.0 | 9444 | 2025-12-28 03:19:04 | MASTER-Kislovodsk | (10h 02m 44.12s , +52d 57m 20.4s) | C | 60 | 17.2 | 9532 | 2025-12-28 03:20:31 | MASTER-Kislovodsk | (10h 10m 51.42s , +52d 38m 02.1s) | C | 60 | 12.5 | 9532 | 2025-12-28 03:20:31 | MASTER-Kislovodsk | (10h 02m 52.79s , +52d 57m 16.2s) | C | 60 | 13.0 | 9727 | 2025-12-28 03:23:46 | MASTER-Kislovodsk | (10h 12m 38.78s , +46d 54m 03.4s) | C | 60 | 17.3 | 9727 | 2025-12-28 03:23:46 | MASTER-Kislovodsk | (10h 06m 01.84s , +47d 14m 22.2s) | C | 60 | 17.4 | 9838 | 2025-12-28 03:25:37 | MASTER-Kislovodsk | (10h 23m 05.28s , +50d 45m 00.9s) | C | 60 | 16.5 | 9838 | 2025-12-28 03:25:37 | MASTER-Kislovodsk | (10h 15m 55.30s , +51d 04m 37.3s) | C | 60 | 17.1 | 9938 | 2025-12-28 03:27:18 | MASTER-Kislovodsk | (09h 56m 44.01s , +54d 31m 10.7s) | C | 60 | 16.9 | 9938 | 2025-12-28 03:27:18 | MASTER-Kislovodsk | (09h 48m 57.16s , +54d 50m 21.4s) | C | 60 | 17.1 | 10035 | 2025-12-28 03:28:55 | MASTER-Kislovodsk | (10h 02m 38.82s , +45d 21m 03.2s) | C | 60 | 17.2 | 10035 | 2025-12-28 03:28:55 | MASTER-Kislovodsk | (10h 09m 00.78s , +45d 00m 24.6s) | C | 60 | 17.3 | 10131 | 2025-12-28 03:30:30 | MASTER-Kislovodsk | (10h 29m 50.64s , +52d 37m 23.2s) | C | 60 | 16.3 | 10131 | 2025-12-28 03:30:30 | MASTER-Kislovodsk | (10h 22m 22.44s , +52d 56m 41.9s) | C | 60 | 16.8 | 10425 | 2025-12-28 03:35:24 | MASTER-Kislovodsk | (10h 12m 34.39s , +46d 54m 15.9s) | C | 60 | 16.4 | 10425 | 2025-12-28 03:35:25 | MASTER-Kislovodsk | (10h 05m 58.49s , +47d 14m 53.3s) | C | 60 | 17.1 | 10525 | 2025-12-28 03:37:05 | MASTER-Kislovodsk | (10h 22m 54.27s , +50d 44m 24.8s) | C | 60 | 16.2 | 10525 | 2025-12-28 03:37:05 | MASTER-Kislovodsk | (10h 15m 45.45s , +51d 04m 05.3s) | C | 60 | 16.8 | 10625 | 2025-12-28 03:38:45 | MASTER-Kislovodsk | (10h 23m 30.87s , +47d 14m 23.6s) | C | 60 | 16.5 | 10625 | 2025-12-28 03:38:45 | MASTER-Kislovodsk | (10h 30m 07.84s , +46d 54m 02.6s) | C | 60 | 15.8 | 10723 | 2025-12-28 03:40:23 | MASTER-Kislovodsk | (10h 02m 34.91s , +45d 21m 28.3s) | C | 60 | 16.7 | 10723 | 2025-12-28 03:40:23 | MASTER-Kislovodsk | (10h 08m 55.83s , +45d 00m 49.5s) | C | 60 | 16.3 | 10822 | 2025-12-28 03:42:02 | MASTER-Kislovodsk | (10h 29m 51.19s , +52d 36m 51.2s) | C | 60 | 15.5 | 10822 | 2025-12-28 03:42:02 | MASTER-Kislovodsk | (10h 22m 23.72s , +52d 56m 14.6s) | C | 60 | 16.2 | 10919 | 2025-12-28 03:43:39 | MASTER-Kislovodsk | (10h 09m 41.91s , +54d 51m 05.3s) | C | 60 | 16.2 | 10919 | 2025-12-28 03:43:39 | MASTER-Kislovodsk | (10h 17m 29.19s , +54d 31m 54.0s) | C | 60 | 15.6 | 11205 | 2025-12-28 03:48:25 | MASTER-Kislovodsk | (10h 22m 53.42s , +50d 43m 55.8s) | C | 60 | 15.1 | 11205 | 2025-12-28 03:48:25 | MASTER-Kislovodsk | (10h 15m 44.95s , +51d 03m 36.9s) | C | 60 | 16.1 | 11323 | 2025-12-28 03:50:23 | MASTER-Kislovodsk | (10h 23m 29.69s , +47d 13m 59.1s) | C | 60 | 16.1 | 11323 | 2025-12-28 03:50:23 | MASTER-Kislovodsk | (10h 30m 06.25s , +46d 53m 23.4s) | C | 60 | 15.2 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43248. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41337] The EP-WXT trigger 01709250662 is likely a flaring star
by GCN Circulars 28 Dec '25

28 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43247 SUBJECT: The EP-WXT trigger 01709250662 is likely a flaring star DATE: 25/12/28 01:29:14 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.-H. I. Yin (HKU), J. P. Feng, B. Zhang (USTC), H. C. Ding, T. Wu (AHNU), D. Z. Du (ZJU), R. X. Hu (WHU), and W. D. Zhang (NAO,CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709250662 at the time of 2025-12-27T16:37:01, is likely a stellar flare associated with PM J11474+6644. The estimated flux of the flare is around 1.8×10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 9.5×10^30 erg/s. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/43247. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41336] GRB 251228A: Fermi GBM Final Real-time Localization
by GCN Circulars 28 Dec '25

28 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43246 SUBJECT: GRB 251228A: Fermi GBM Final Real-time Localization DATE: 25/12/28 00:52:53 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely SHORT GRB At 00:42:10 UT on 28 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251228A (trigger 788575335.25706 / 251228029). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 150.2, Dec = 49.8 (J2000 degrees, equivalent to J2000 10h 00m, 49d 47'), with a statistical uncertainty of 10.7 degrees. The angle from the Fermi LAT boresight is 107.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251228029/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251228029/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251228029/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43246. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41335] GRB 251226A: SVOM/GRM observation
by GCN Circulars 27 Dec '25

27 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43245 SUBJECT: GRB 251226A: SVOM/GRM observation DATE: 25/12/27 17:34:44 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Wen-Jun Tan, Xue-Yuan Zao, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Olivier GODET (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight GRB 251226A (SVOM trigger reference: sb25122601) at 2025-12-26T08:01:05.000 UTC (T0), which is also detected by GECAM-B (Wang et al., GCN#43244) and HXMT. With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a precursor followed by a main emission with a T90 of 58.7 +9.0/-9.4 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251226A.png In addition, the position of this burst, as determined by GECAM-B (RA= 260.2, DEC= 47.0, ERR=9.1), is located at about 125 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-3 to T0+100 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.29 +0.22/-0.19 and the cutoff energy, parameterized as Epeak, is 632 +279/-146 keV. The event fluence (10-1000 keV) in this time interval is (4.33 +0.20/-0.21)E-05 erg/cm^2. The 1s peak spectrum, measured from T0+3 to T0+4 s, is also best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.18 +0.27/-0.20 and the cutoff energy, parameterized as Epeak, is 1520 +122/-56 keV. The flux (10-1000 keV) in this time interval is (2.61 +0.17/-0.17)E-06 erg/cm^2/s. The localization of GRB 251226A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251226A_amati.png And the localization in the 'Yonetoku' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251226A_yonetoku.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/43245. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41334] GRB 251226A: GECAM-B detection
by GCN Circulars 27 Dec '25

27 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43244 SUBJECT: GRB 251226A: GECAM-B detection DATE: 25/12/27 17:22:35 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Wen-Jun Tan, Xue-Yuan Zao, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by a long burst GRB 251226A, at 2025-12-26T08:01:02.550 UTC (denoted as T0), which is also detected by SVOM/GRM and HXMT. According to the GECAM-B light curve in about 70-6000 keV, this burst mainly consists of a precursor-like pulse followed by a multi-pulses main emission with a duration (T90) of 35.9 +3.4/-6.0 s. We note that the quiescent time between the precursor-like pulse and the main emission is relatively short. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb251226A.png GECAM-B in-flight localization of this burst is (J2000): Ra: 260.2 deg Dec: 47.0 deg Err: 9.1 deg (1-sigma, statistical only) We note that the localization may be improved since this burst is not detected by Fermi/GBM. Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/43244. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41333] SVOM GRB251227.07: Global MASTER-Net observations report
by GCN Circulars 27 Dec '25

27 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43243 SUBJECT: SVOM GRB251227.07: Global MASTER-Net observations report DATE: 25/12/27 03:56:36 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the SVOM GRB251227.07 (trigger No 1766799801,08h 24m 32.81s , +02d 47m 22.9s, R=1) errorbox 13 sec after notice time and 47 sec after trigger time at 2025-12-27 01:44:08 UT, with upper limit up to 16.9 mag. The observations began at zenith distance = 52 deg. The sun altitude is -31.3 deg. MASTER-OAFA robotic telescope located in Argentina (OAFA observatory of San Juan National University) started inspect of the SVOM GRB251227.07 errorbox 107 sec after notice time and 141 sec after trigger time at 2025-12-27 01:45:42 UT, with upper limit up to 19.4 mag. The observations began at zenith distance = 77 deg. The sun altitude is -22.1 deg. The galactic latitude b = 22 deg., longitude l = 222 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3086623 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 52 | 2025-12-27 01:44:08 | MASTER-Kislovodsk | (08h 23m 49.79s , +02d 54m 44.7s) | P- | 10 | 15.5 | 52 | 2025-12-27 01:44:08 | MASTER-Kislovodsk | (08h 23m 44.07s , +03d 16m 39.6s) | P| | 10 | 13.5 | 92 | 2025-12-27 01:44:42 | MASTER-Kislovodsk | (08h 24m 08.87s , +02d 54m 43.9s) | P- | 20 | 12.4 | 141 | 2025-12-27 01:45:27 | MASTER-Kislovodsk | (08h 24m 38.91s , +02d 54m 44.1s) | P- | 30 | 12.2 | 156 | 2025-12-27 01:45:42 | MASTER-OAFA | (08h 24m 30.53s , +02d 53m 39.1s) | C | 30 | 14.0 | 197 | 2025-12-27 01:46:18 | MASTER-OAFA | (08h 24m 30.76s , +02d 53m 43.8s) | C | 40 | 14.5 | 244 | 2025-12-27 01:47:05 | MASTER-OAFA | (08h 24m 30.96s , +02d 53m 48.7s) | C | 40 | 15.1 | 295 | 2025-12-27 01:47:51 | MASTER-OAFA | (08h 24m 31.13s , +02d 53m 53.9s) | C | 50 | 15.6 | 336 | 2025-12-27 01:48:26 | MASTER-Kislovodsk | (08h 24m 06.38s , +03d 13m 43.2s) | C | 60 | 16.7 | 336 | 2025-12-27 01:48:26 | MASTER-Kislovodsk | (08h 20m 01.59s , +03d 34m 00.8s) | C | 60 | 16.9 | 361 | 2025-12-27 01:48:47 | MASTER-OAFA | (08h 24m 31.36s , +02d 54m 00.5s) | C | 70 | 16.1 | 443 | 2025-12-27 01:50:03 | MASTER-OAFA | (08h 24m 31.60s , +02d 54m 07.7s) | C | 80 | 16.4 | 539 | 2025-12-27 01:51:29 | MASTER-OAFA | (08h 24m 31.92s , +02d 54m 16.2s) | C | 100 | 16.8 | 655 | 2025-12-27 01:53:15 | MASTER-OAFA | (08h 24m 32.18s , +02d 54m 25.7s) | C | 120 | 17.1 | 791 | 2025-12-27 01:55:21 | MASTER-OAFA | (08h 24m 32.48s , +02d 54m 36.5s) | C | 140 | 17.3 | 953 | 2025-12-27 01:57:48 | MASTER-OAFA | (08h 24m 32.88s , +02d 54m 49.4s) | C | 170 | 17.5 | 1074 | 2025-12-27 02:00:44 | MASTER-OAFA | (08h 24m 33.15s , +02d 54m 58.8s) | C | 60 | 17.7 | 1139 | 2025-12-27 02:01:50 | MASTER-OAFA | (08h 24m 33.27s , +02d 55m 03.5s) | C | 60 | 17.9 | 1205 | 2025-12-27 02:02:55 | MASTER-OAFA | (08h 24m 33.41s , +02d 55m 08.5s) | C | 60 | 17.9 | 1271 | 2025-12-27 02:04:01 | MASTER-OAFA | (08h 24m 33.56s , +02d 55m 13.6s) | C | 60 | 18.0 | 1336 | 2025-12-27 02:05:06 | MASTER-OAFA | (08h 24m 33.67s , +02d 55m 18.3s) | C | 60 | 18.0 | 1401 | 2025-12-27 02:06:12 | MASTER-OAFA | (08h 24m 33.79s , +02d 55m 23.2s) | C | 60 | 18.1 | 1467 | 2025-12-27 02:07:17 | MASTER-OAFA | (08h 24m 33.91s , +02d 55m 28.1s) | C | 60 | 18.1 | 1532 | 2025-12-27 02:08:23 | MASTER-OAFA | (08h 24m 34.04s , +02d 55m 33.0s) | C | 60 | 18.2 | 1598 | 2025-12-27 02:09:28 | MASTER-OAFA | (08h 24m 34.15s , +02d 55m 37.9s) | C | 60 | 18.3 | 1664 | 2025-12-27 02:10:34 | MASTER-OAFA | (08h 24m 34.25s , +02d 55m 42.5s) | C | 60 | 18.4 | 1729 | 2025-12-27 02:11:40 | MASTER-OAFA | (08h 24m 34.40s , +02d 55m 47.4s) | C | 60 | 18.4 | 1795 | 2025-12-27 02:12:45 | MASTER-OAFA | (08h 24m 34.55s , +02d 55m 52.2s) | C | 60 | 18.4 | 1861 | 2025-12-27 02:13:51 | MASTER-OAFA | (08h 24m 34.63s , +02d 55m 56.7s) | C | 60 | 18.4 | 1926 | 2025-12-27 02:14:57 | MASTER-OAFA | (08h 24m 34.75s , +02d 56m 01.5s) | C | 60 | 18.5 | 1991 | 2025-12-27 02:16:02 | MASTER-OAFA | (08h 24m 34.86s , +02d 56m 05.9s) | C | 60 | 18.4 | 2061 | 2025-12-27 02:17:12 | MASTER-OAFA | (08h 24m 34.97s , +02d 56m 10.6s) | C | 60 | 18.5 | 2126 | 2025-12-27 02:18:17 | MASTER-OAFA | (08h 24m 35.09s , +02d 56m 15.1s) | C | 60 | 18.4 | 2192 | 2025-12-27 02:19:23 | MASTER-OAFA | (08h 24m 35.17s , +02d 56m 19.3s) | C | 60 | 18.6 | 2259 | 2025-12-27 02:20:29 | MASTER-OAFA | (08h 24m 35.30s , +02d 56m 24.0s) | C | 60 | 18.6 | 2324 | 2025-12-27 02:21:34 | MASTER-OAFA | (08h 24m 35.41s , +02d 56m 28.3s) | C | 60 | 18.6 | 2390 | 2025-12-27 02:22:40 | MASTER-OAFA | (08h 24m 35.47s , +02d 56m 32.6s) | C | 60 | 18.6 | 2456 | 2025-12-27 02:23:46 | MASTER-OAFA | (08h 24m 35.57s , +02d 56m 36.9s) | C | 60 | 18.7 | 2521 | 2025-12-27 02:24:52 | MASTER-OAFA | (08h 24m 35.68s , +02d 56m 41.3s) | C | 60 | 18.6 | 2586 | 2025-12-27 02:25:57 | MASTER-OAFA | (08h 24m 35.77s , +02d 56m 45.7s) | C | 60 | 18.6 | 2653 | 2025-12-27 02:27:03 | MASTER-OAFA | (08h 24m 35.87s , +02d 56m 49.9s) | C | 60 | 18.7 | 2718 | 2025-12-27 02:28:09 | MASTER-OAFA | (08h 24m 35.96s , +02d 56m 54.2s) | C | 60 | 18.7 | 2784 | 2025-12-27 02:29:14 | MASTER-OAFA | (08h 24m 36.07s , +02d 56m 58.5s) | C | 60 | 18.7 | 2850 | 2025-12-27 02:30:20 | MASTER-OAFA | (08h 24m 36.16s , +02d 57m 02.6s) | C | 60 | 18.7 | 2916 | 2025-12-27 02:31:26 | MASTER-OAFA | (08h 24m 36.25s , +02d 57m 06.7s) | C | 60 | 18.7 | 2981 | 2025-12-27 02:32:31 | MASTER-OAFA | (08h 24m 36.33s , +02d 57m 10.7s) | C | 60 | 18.8 | 3048 | 2025-12-27 02:33:38 | MASTER-OAFA | (08h 24m 36.42s , +02d 57m 14.8s) | C | 60 | 18.8 | 3113 | 2025-12-27 02:34:43 | MASTER-OAFA | (08h 24m 36.49s , +02d 57m 18.6s) | C | 60 | 18.9 | 3178 | 2025-12-27 02:35:49 | MASTER-OAFA | (08h 24m 36.57s , +02d 57m 22.4s) | C | 60 | 18.9 | 3244 | 2025-12-27 02:36:55 | MASTER-OAFA | (08h 24m 36.65s , +02d 57m 26.4s) | C | 60 | 18.8 | 3310 | 2025-12-27 02:38:01 | MASTER-OAFA | (08h 24m 36.72s , +02d 57m 30.5s) | C | 60 | 18.9 | 3376 | 2025-12-27 02:39:06 | MASTER-OAFA | (08h 24m 36.78s , +02d 57m 34.2s) | C | 60 | 18.9 | 3442 | 2025-12-27 02:40:13 | MASTER-OAFA | (08h 24m 36.85s , +02d 57m 38.0s) | C | 60 | 18.8 | 3507 | 2025-12-27 02:41:18 | MASTER-OAFA | (08h 24m 36.91s , +02d 57m 41.8s) | C | 60 | 18.9 | 3572 | 2025-12-27 02:42:23 | MASTER-OAFA | (08h 24m 36.98s , +02d 57m 45.5s) | C | 60 | 18.9 | 3638 | 2025-12-27 02:43:29 | MASTER-OAFA | (08h 24m 37.06s , +02d 57m 49.3s) | C | 60 | 18.9 | 3704 | 2025-12-27 02:44:34 | MASTER-OAFA | (08h 24m 37.10s , +02d 57m 53.0s) | C | 60 | 18.9 | 3769 | 2025-12-27 02:45:40 | MASTER-OAFA | (08h 24m 37.15s , +02d 57m 56.6s) | C | 60 | 18.9 | 3838 | 2025-12-27 02:46:49 | MASTER-OAFA | (08h 24m 37.22s , +02d 58m 00.5s) | C | 60 | 19.0 | 3904 | 2025-12-27 02:47:54 | MASTER-OAFA | (08h 24m 37.27s , +02d 58m 04.1s) | C | 60 | 18.9 | 3969 | 2025-12-27 02:49:00 | MASTER-OAFA | (08h 24m 37.34s , +02d 58m 07.8s) | C | 60 | 18.9 | 4035 | 2025-12-27 02:50:05 | MASTER-OAFA | (08h 24m 37.39s , +02d 58m 11.4s) | C | 60 | 18.9 | 4100 | 2025-12-27 02:51:11 | MASTER-OAFA | (08h 24m 37.44s , +02d 58m 14.8s) | C | 60 | 19.0 | 4166 | 2025-12-27 02:52:16 | MASTER-OAFA | (08h 24m 37.50s , +02d 58m 18.2s) | C | 60 | 19.0 | 4232 | 2025-12-27 02:53:22 | MASTER-OAFA | (08h 24m 37.55s , +02d 58m 21.4s) | C | 60 | 19.0 | 4297 | 2025-12-27 02:54:28 | MASTER-OAFA | (08h 24m 37.58s , +02d 58m 24.7s) | C | 60 | 19.0 | 4363 | 2025-12-27 02:55:33 | MASTER-OAFA | (08h 24m 37.62s , +02d 58m 27.9s) | C | 60 | 19.1 | 4428 | 2025-12-27 02:56:39 | MASTER-OAFA | (08h 24m 37.67s , +02d 58m 31.2s) | C | 60 | 19.1 | 4494 | 2025-12-27 02:57:44 | MASTER-OAFA | (08h 24m 37.71s , +02d 58m 34.4s) | C | 60 | 19.0 | 4559 | 2025-12-27 02:58:50 | MASTER-OAFA | (08h 24m 37.75s , +02d 58m 37.5s) | C | 60 | 19.1 | 4626 | 2025-12-27 02:59:57 | MASTER-OAFA | (08h 24m 37.78s , +02d 58m 40.7s) | C | 60 | 19.0 | 4692 | 2025-12-27 03:01:02 | MASTER-OAFA | (08h 24m 37.82s , +02d 58m 43.9s) | C | 60 | 19.1 | 4757 | 2025-12-27 03:02:08 | MASTER-OAFA | (08h 24m 37.84s , +02d 58m 47.0s) | C | 60 | 19.1 | 4823 | 2025-12-27 03:03:14 | MASTER-OAFA | (08h 24m 37.87s , +02d 58m 49.9s) | C | 60 | 19.1 | 4888 | 2025-12-27 03:04:19 | MASTER-OAFA | (08h 24m 37.91s , +02d 58m 52.8s) | C | 60 | 19.1 | 4954 | 2025-12-27 03:05:24 | MASTER-OAFA | (08h 24m 37.93s , +02d 58m 55.8s) | C | 60 | 19.1 | 5020 | 2025-12-27 03:06:30 | MASTER-OAFA | (08h 24m 37.96s , +02d 58m 58.7s) | C | 60 | 19.1 | 5085 | 2025-12-27 03:07:36 | MASTER-OAFA | (08h 24m 38.00s , +02d 59m 01.7s) | C | 60 | 19.1 | 5151 | 2025-12-27 03:08:41 | MASTER-OAFA | (08h 24m 38.00s , +02d 59m 04.3s) | C | 60 | 19.1 | 5217 | 2025-12-27 03:09:48 | MASTER-OAFA | (08h 24m 38.01s , +02d 59m 07.0s) | C | 60 | 19.1 | 5283 | 2025-12-27 03:10:53 | MASTER-OAFA | (08h 24m 38.04s , +02d 59m 09.9s) | C | 60 | 19.2 | 5348 | 2025-12-27 03:11:59 | MASTER-OAFA | (08h 24m 38.07s , +02d 59m 12.4s) | C | 60 | 19.1 | 5415 | 2025-12-27 03:13:05 | MASTER-OAFA | (08h 24m 38.09s , +02d 59m 15.0s) | C | 60 | 19.2 | 5480 | 2025-12-27 03:14:11 | MASTER-OAFA | (08h 24m 38.10s , +02d 59m 17.7s) | C | 60 | 19.1 | 5546 | 2025-12-27 03:15:16 | MASTER-OAFA | (08h 24m 38.10s , +02d 59m 20.4s) | C | 60 | 19.1 | 5613 | 2025-12-27 03:16:24 | MASTER-OAFA | (08h 24m 38.08s , +02d 59m 22.7s) | C | 60 | 19.2 | 5679 | 2025-12-27 03:17:29 | MASTER-OAFA | (08h 24m 38.08s , +02d 59m 25.1s) | C | 60 | 19.2 | 5744 | 2025-12-27 03:18:34 | MASTER-OAFA | (08h 24m 38.09s , +02d 59m 27.5s) | C | 60 | 19.2 | 5810 | 2025-12-27 03:19:40 | MASTER-OAFA | (08h 24m 38.09s , +02d 59m 29.9s) | C | 60 | 19.2 | 5876 | 2025-12-27 03:20:46 | MASTER-OAFA | (08h 24m 38.09s , +02d 59m 32.1s) | C | 60 | 19.2 | 5941 | 2025-12-27 03:21:52 | MASTER-OAFA | (08h 24m 38.07s , +02d 59m 34.4s) | C | 60 | 19.3 | 6007 | 2025-12-27 03:22:58 | MASTER-OAFA | (08h 24m 38.05s , +02d 59m 36.7s) | C | 60 | 19.3 | 6073 | 2025-12-27 03:24:04 | MASTER-OAFA | (08h 24m 38.03s , +02d 59m 39.0s) | C | 60 | 19.2 | 6139 | 2025-12-27 03:25:09 | MASTER-OAFA | (08h 24m 38.01s , +02d 59m 41.2s) | C | 60 | 19.3 | 6205 | 2025-12-27 03:26:15 | MASTER-OAFA | (08h 24m 37.99s , +02d 59m 43.3s) | C | 60 | 19.3 | 6270 | 2025-12-27 03:27:20 | MASTER-OAFA | (08h 24m 37.98s , +02d 59m 45.5s) | C | 60 | 19.3 | 6335 | 2025-12-27 03:28:26 | MASTER-OAFA | (08h 24m 37.94s , +02d 59m 47.5s) | C | 60 | 19.3 | 6401 | 2025-12-27 03:29:31 | MASTER-OAFA | (08h 24m 37.94s , +02d 59m 49.7s) | C | 60 | 19.3 | 6466 | 2025-12-27 03:30:36 | MASTER-OAFA | (08h 24m 37.93s , +02d 59m 51.8s) | C | 60 | 19.3 | 6531 | 2025-12-27 03:31:42 | MASTER-OAFA | (08h 24m 37.90s , +02d 59m 53.7s) | C | 60 | 19.3 | 6597 | 2025-12-27 03:32:48 | MASTER-OAFA | (08h 24m 37.86s , +02d 59m 55.7s) | C | 60 | 19.3 | 6663 | 2025-12-27 03:33:53 | MASTER-OAFA | (08h 24m 37.82s , +02d 59m 57.5s) | C | 60 | 19.3 | 6728 | 2025-12-27 03:34:59 | MASTER-OAFA | (08h 24m 37.78s , +02d 59m 59.3s) | C | 60 | 19.3 | 6794 | 2025-12-27 03:36:05 | MASTER-OAFA | (08h 24m 37.74s , +03d 00m 01.2s) | C | 60 | 19.3 | 6859 | 2025-12-27 03:37:10 | MASTER-OAFA | (08h 24m 37.70s , +03d 00m 03.1s) | C | 60 | 19.3 | 6925 | 2025-12-27 03:38:15 | MASTER-OAFA | (08h 24m 37.65s , +03d 00m 04.7s) | C | 60 | 19.4 | 6991 | 2025-12-27 03:39:21 | MASTER-OAFA | (08h 24m 37.61s , +03d 00m 06.5s) | C | 60 | 19.4 | 7056 | 2025-12-27 03:40:27 | MASTER-OAFA | (08h 24m 37.56s , +03d 00m 07.9s) | C | 60 | 19.4 | 7122 | 2025-12-27 03:41:33 | MASTER-OAFA | (08h 24m 37.53s , +03d 00m 09.5s) | C | 60 | 19.3 | 7188 | 2025-12-27 03:42:39 | MASTER-OAFA | (08h 24m 37.47s , +03d 00m 10.9s) | C | 60 | 19.3 | 7254 | 2025-12-27 03:43:44 | MASTER-OAFA | (08h 24m 37.42s , +03d 00m 12.3s) | C | 60 | 19.3 | 7320 | 2025-12-27 03:44:50 | MASTER-OAFA | (08h 24m 37.37s , +03d 00m 13.7s) | C | 60 | 19.3 | 7442 | 2025-12-27 03:46:53 | MASTER-OAFA | (08h 24m 37.49s , +03d 02m 16.4s) | C | 60 | 18.5 | 7508 | 2025-12-27 03:47:58 | MASTER-OAFA | (08h 24m 37.46s , +03d 02m 17.6s) | C | 60 | 19.4 | 7573 | 2025-12-27 03:49:04 | MASTER-OAFA | (08h 24m 37.40s , +03d 02m 18.7s) | C | 60 | 19.3 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43243. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41332] SVOM GRB251227.07: Global MASTER-Net observations report
by GCN Circulars 27 Dec '25

27 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43243 SUBJECT: SVOM GRB251227.07: Global MASTER-Net observations report DATE: 25/12/27 03:56:36 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the SVOM GRB251227.07 (trigger No 1766799801,08h 24m 32.81s , +02d 47m 22.9s, R=1) errorbox 13 sec after notice time and 47 sec after trigger time at 2025-12-27 01:44:08 UT, with upper limit up to 16.9 mag. The observations began at zenith distance = 52 deg. The sun altitude is -31.3 deg. MASTER-OAFA robotic telescope located in Argentina (OAFA observatory of San Juan National University) started inspect of the SVOM GRB251227.07 errorbox 107 sec after notice time and 141 sec after trigger time at 2025-12-27 01:45:42 UT, with upper limit up to 19.4 mag. The observations began at zenith distance = 77 deg. The sun altitude is -22.1 deg. The galactic latitude b = 22 deg., longitude l = 222 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3086623 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 52 | 2025-12-27 01:44:08 | MASTER-Kislovodsk | (08h 23m 49.79s , +02d 54m 44.7s) | P- | 10 | 15.5 | 52 | 2025-12-27 01:44:08 | MASTER-Kislovodsk | (08h 23m 44.07s , +03d 16m 39.6s) | P| | 10 | 13.5 | 92 | 2025-12-27 01:44:42 | MASTER-Kislovodsk | (08h 24m 08.87s , +02d 54m 43.9s) | P- | 20 | 12.4 | 141 | 2025-12-27 01:45:27 | MASTER-Kislovodsk | (08h 24m 38.91s , +02d 54m 44.1s) | P- | 30 | 12.2 | 156 | 2025-12-27 01:45:42 | MASTER-OAFA | (08h 24m 30.53s , +02d 53m 39.1s) | C | 30 | 14.0 | 197 | 2025-12-27 01:46:18 | MASTER-OAFA | (08h 24m 30.76s , +02d 53m 43.8s) | C | 40 | 14.5 | 244 | 2025-12-27 01:47:05 | MASTER-OAFA | (08h 24m 30.96s , +02d 53m 48.7s) | C | 40 | 15.1 | 295 | 2025-12-27 01:47:51 | MASTER-OAFA | (08h 24m 31.13s , +02d 53m 53.9s) | C | 50 | 15.6 | 336 | 2025-12-27 01:48:26 | MASTER-Kislovodsk | (08h 24m 06.38s , +03d 13m 43.2s) | C | 60 | 16.7 | 336 | 2025-12-27 01:48:26 | MASTER-Kislovodsk | (08h 20m 01.59s , +03d 34m 00.8s) | C | 60 | 16.9 | 361 | 2025-12-27 01:48:47 | MASTER-OAFA | (08h 24m 31.36s , +02d 54m 00.5s) | C | 70 | 16.1 | 443 | 2025-12-27 01:50:03 | MASTER-OAFA | (08h 24m 31.60s , +02d 54m 07.7s) | C | 80 | 16.4 | 539 | 2025-12-27 01:51:29 | MASTER-OAFA | (08h 24m 31.92s , +02d 54m 16.2s) | C | 100 | 16.8 | 655 | 2025-12-27 01:53:15 | MASTER-OAFA | (08h 24m 32.18s , +02d 54m 25.7s) | C | 120 | 17.1 | 791 | 2025-12-27 01:55:21 | MASTER-OAFA | (08h 24m 32.48s , +02d 54m 36.5s) | C | 140 | 17.3 | 953 | 2025-12-27 01:57:48 | MASTER-OAFA | (08h 24m 32.88s , +02d 54m 49.4s) | C | 170 | 17.5 | 1074 | 2025-12-27 02:00:44 | MASTER-OAFA | (08h 24m 33.15s , +02d 54m 58.8s) | C | 60 | 17.7 | 1139 | 2025-12-27 02:01:50 | MASTER-OAFA | (08h 24m 33.27s , +02d 55m 03.5s) | C | 60 | 17.9 | 1205 | 2025-12-27 02:02:55 | MASTER-OAFA | (08h 24m 33.41s , +02d 55m 08.5s) | C | 60 | 17.9 | 1271 | 2025-12-27 02:04:01 | MASTER-OAFA | (08h 24m 33.56s , +02d 55m 13.6s) | C | 60 | 18.0 | 1336 | 2025-12-27 02:05:06 | MASTER-OAFA | (08h 24m 33.67s , +02d 55m 18.3s) | C | 60 | 18.0 | 1401 | 2025-12-27 02:06:12 | MASTER-OAFA | (08h 24m 33.79s , +02d 55m 23.2s) | C | 60 | 18.1 | 1467 | 2025-12-27 02:07:17 | MASTER-OAFA | (08h 24m 33.91s , +02d 55m 28.1s) | C | 60 | 18.1 | 1532 | 2025-12-27 02:08:23 | MASTER-OAFA | (08h 24m 34.04s , +02d 55m 33.0s) | C | 60 | 18.2 | 1598 | 2025-12-27 02:09:28 | MASTER-OAFA | (08h 24m 34.15s , +02d 55m 37.9s) | C | 60 | 18.3 | 1664 | 2025-12-27 02:10:34 | MASTER-OAFA | (08h 24m 34.25s , +02d 55m 42.5s) | C | 60 | 18.4 | 1729 | 2025-12-27 02:11:40 | MASTER-OAFA | (08h 24m 34.40s , +02d 55m 47.4s) | C | 60 | 18.4 | 1795 | 2025-12-27 02:12:45 | MASTER-OAFA | (08h 24m 34.55s , +02d 55m 52.2s) | C | 60 | 18.4 | 1861 | 2025-12-27 02:13:51 | MASTER-OAFA | (08h 24m 34.63s , +02d 55m 56.7s) | C | 60 | 18.4 | 1926 | 2025-12-27 02:14:57 | MASTER-OAFA | (08h 24m 34.75s , +02d 56m 01.5s) | C | 60 | 18.5 | 1991 | 2025-12-27 02:16:02 | MASTER-OAFA | (08h 24m 34.86s , +02d 56m 05.9s) | C | 60 | 18.4 | 2061 | 2025-12-27 02:17:12 | MASTER-OAFA | (08h 24m 34.97s , +02d 56m 10.6s) | C | 60 | 18.5 | 2126 | 2025-12-27 02:18:17 | MASTER-OAFA | (08h 24m 35.09s , +02d 56m 15.1s) | C | 60 | 18.4 | 2192 | 2025-12-27 02:19:23 | MASTER-OAFA | (08h 24m 35.17s , +02d 56m 19.3s) | C | 60 | 18.6 | 2259 | 2025-12-27 02:20:29 | MASTER-OAFA | (08h 24m 35.30s , +02d 56m 24.0s) | C | 60 | 18.6 | 2324 | 2025-12-27 02:21:34 | MASTER-OAFA | (08h 24m 35.41s , +02d 56m 28.3s) | C | 60 | 18.6 | 2390 | 2025-12-27 02:22:40 | MASTER-OAFA | (08h 24m 35.47s , +02d 56m 32.6s) | C | 60 | 18.6 | 2456 | 2025-12-27 02:23:46 | MASTER-OAFA | (08h 24m 35.57s , +02d 56m 36.9s) | C | 60 | 18.7 | 2521 | 2025-12-27 02:24:52 | MASTER-OAFA | (08h 24m 35.68s , +02d 56m 41.3s) | C | 60 | 18.6 | 2586 | 2025-12-27 02:25:57 | MASTER-OAFA | (08h 24m 35.77s , +02d 56m 45.7s) | C | 60 | 18.6 | 2653 | 2025-12-27 02:27:03 | MASTER-OAFA | (08h 24m 35.87s , +02d 56m 49.9s) | C | 60 | 18.7 | 2718 | 2025-12-27 02:28:09 | MASTER-OAFA | (08h 24m 35.96s , +02d 56m 54.2s) | C | 60 | 18.7 | 2784 | 2025-12-27 02:29:14 | MASTER-OAFA | (08h 24m 36.07s , +02d 56m 58.5s) | C | 60 | 18.7 | 2850 | 2025-12-27 02:30:20 | MASTER-OAFA | (08h 24m 36.16s , +02d 57m 02.6s) | C | 60 | 18.7 | 2916 | 2025-12-27 02:31:26 | MASTER-OAFA | (08h 24m 36.25s , +02d 57m 06.7s) | C | 60 | 18.7 | 2981 | 2025-12-27 02:32:31 | MASTER-OAFA | (08h 24m 36.33s , +02d 57m 10.7s) | C | 60 | 18.8 | 3048 | 2025-12-27 02:33:38 | MASTER-OAFA | (08h 24m 36.42s , +02d 57m 14.8s) | C | 60 | 18.8 | 3113 | 2025-12-27 02:34:43 | MASTER-OAFA | (08h 24m 36.49s , +02d 57m 18.6s) | C | 60 | 18.9 | 3178 | 2025-12-27 02:35:49 | MASTER-OAFA | (08h 24m 36.57s , +02d 57m 22.4s) | C | 60 | 18.9 | 3244 | 2025-12-27 02:36:55 | MASTER-OAFA | (08h 24m 36.65s , +02d 57m 26.4s) | C | 60 | 18.8 | 3310 | 2025-12-27 02:38:01 | MASTER-OAFA | (08h 24m 36.72s , +02d 57m 30.5s) | C | 60 | 18.9 | 3376 | 2025-12-27 02:39:06 | MASTER-OAFA | (08h 24m 36.78s , +02d 57m 34.2s) | C | 60 | 18.9 | 3442 | 2025-12-27 02:40:13 | MASTER-OAFA | (08h 24m 36.85s , +02d 57m 38.0s) | C | 60 | 18.8 | 3507 | 2025-12-27 02:41:18 | MASTER-OAFA | (08h 24m 36.91s , +02d 57m 41.8s) | C | 60 | 18.9 | 3572 | 2025-12-27 02:42:23 | MASTER-OAFA | (08h 24m 36.98s , +02d 57m 45.5s) | C | 60 | 18.9 | 3638 | 2025-12-27 02:43:29 | MASTER-OAFA | (08h 24m 37.06s , +02d 57m 49.3s) | C | 60 | 18.9 | 3704 | 2025-12-27 02:44:34 | MASTER-OAFA | (08h 24m 37.10s , +02d 57m 53.0s) | C | 60 | 18.9 | 3769 | 2025-12-27 02:45:40 | MASTER-OAFA | (08h 24m 37.15s , +02d 57m 56.6s) | C | 60 | 18.9 | 3838 | 2025-12-27 02:46:49 | MASTER-OAFA | (08h 24m 37.22s , +02d 58m 00.5s) | C | 60 | 19.0 | 3904 | 2025-12-27 02:47:54 | MASTER-OAFA | (08h 24m 37.27s , +02d 58m 04.1s) | C | 60 | 18.9 | 3969 | 2025-12-27 02:49:00 | MASTER-OAFA | (08h 24m 37.34s , +02d 58m 07.8s) | C | 60 | 18.9 | 4035 | 2025-12-27 02:50:05 | MASTER-OAFA | (08h 24m 37.39s , +02d 58m 11.4s) | C | 60 | 18.9 | 4100 | 2025-12-27 02:51:11 | MASTER-OAFA | (08h 24m 37.44s , +02d 58m 14.8s) | C | 60 | 19.0 | 4166 | 2025-12-27 02:52:16 | MASTER-OAFA | (08h 24m 37.50s , +02d 58m 18.2s) | C | 60 | 19.0 | 4232 | 2025-12-27 02:53:22 | MASTER-OAFA | (08h 24m 37.55s , +02d 58m 21.4s) | C | 60 | 19.0 | 4297 | 2025-12-27 02:54:28 | MASTER-OAFA | (08h 24m 37.58s , +02d 58m 24.7s) | C | 60 | 19.0 | 4363 | 2025-12-27 02:55:33 | MASTER-OAFA | (08h 24m 37.62s , +02d 58m 27.9s) | C | 60 | 19.1 | 4428 | 2025-12-27 02:56:39 | MASTER-OAFA | (08h 24m 37.67s , +02d 58m 31.2s) | C | 60 | 19.1 | 4494 | 2025-12-27 02:57:44 | MASTER-OAFA | (08h 24m 37.71s , +02d 58m 34.4s) | C | 60 | 19.0 | 4559 | 2025-12-27 02:58:50 | MASTER-OAFA | (08h 24m 37.75s , +02d 58m 37.5s) | C | 60 | 19.1 | 4626 | 2025-12-27 02:59:57 | MASTER-OAFA | (08h 24m 37.78s , +02d 58m 40.7s) | C | 60 | 19.0 | 4692 | 2025-12-27 03:01:02 | MASTER-OAFA | (08h 24m 37.82s , +02d 58m 43.9s) | C | 60 | 19.1 | 4757 | 2025-12-27 03:02:08 | MASTER-OAFA | (08h 24m 37.84s , +02d 58m 47.0s) | C | 60 | 19.1 | 4823 | 2025-12-27 03:03:14 | MASTER-OAFA | (08h 24m 37.87s , +02d 58m 49.9s) | C | 60 | 19.1 | 4888 | 2025-12-27 03:04:19 | MASTER-OAFA | (08h 24m 37.91s , +02d 58m 52.8s) | C | 60 | 19.1 | 4954 | 2025-12-27 03:05:24 | MASTER-OAFA | (08h 24m 37.93s , +02d 58m 55.8s) | C | 60 | 19.1 | 5020 | 2025-12-27 03:06:30 | MASTER-OAFA | (08h 24m 37.96s , +02d 58m 58.7s) | C | 60 | 19.1 | 5085 | 2025-12-27 03:07:36 | MASTER-OAFA | (08h 24m 38.00s , +02d 59m 01.7s) | C | 60 | 19.1 | 5151 | 2025-12-27 03:08:41 | MASTER-OAFA | (08h 24m 38.00s , +02d 59m 04.3s) | C | 60 | 19.1 | 5217 | 2025-12-27 03:09:48 | MASTER-OAFA | (08h 24m 38.01s , +02d 59m 07.0s) | C | 60 | 19.1 | 5283 | 2025-12-27 03:10:53 | MASTER-OAFA | (08h 24m 38.04s , +02d 59m 09.9s) | C | 60 | 19.2 | 5348 | 2025-12-27 03:11:59 | MASTER-OAFA | (08h 24m 38.07s , +02d 59m 12.4s) | C | 60 | 19.1 | 5415 | 2025-12-27 03:13:05 | MASTER-OAFA | (08h 24m 38.09s , +02d 59m 15.0s) | C | 60 | 19.2 | 5480 | 2025-12-27 03:14:11 | MASTER-OAFA | (08h 24m 38.10s , +02d 59m 17.7s) | C | 60 | 19.1 | 5546 | 2025-12-27 03:15:16 | MASTER-OAFA | (08h 24m 38.10s , +02d 59m 20.4s) | C | 60 | 19.1 | 5613 | 2025-12-27 03:16:24 | MASTER-OAFA | (08h 24m 38.08s , +02d 59m 22.7s) | C | 60 | 19.2 | 5679 | 2025-12-27 03:17:29 | MASTER-OAFA | (08h 24m 38.08s , +02d 59m 25.1s) | C | 60 | 19.2 | 5744 | 2025-12-27 03:18:34 | MASTER-OAFA | (08h 24m 38.09s , +02d 59m 27.5s) | C | 60 | 19.2 | 5810 | 2025-12-27 03:19:40 | MASTER-OAFA | (08h 24m 38.09s , +02d 59m 29.9s) | C | 60 | 19.2 | 5876 | 2025-12-27 03:20:46 | MASTER-OAFA | (08h 24m 38.09s , +02d 59m 32.1s) | C | 60 | 19.2 | 5941 | 2025-12-27 03:21:52 | MASTER-OAFA | (08h 24m 38.07s , +02d 59m 34.4s) | C | 60 | 19.3 | 6007 | 2025-12-27 03:22:58 | MASTER-OAFA | (08h 24m 38.05s , +02d 59m 36.7s) | C | 60 | 19.3 | 6073 | 2025-12-27 03:24:04 | MASTER-OAFA | (08h 24m 38.03s , +02d 59m 39.0s) | C | 60 | 19.2 | 6139 | 2025-12-27 03:25:09 | MASTER-OAFA | (08h 24m 38.01s , +02d 59m 41.2s) | C | 60 | 19.3 | 6205 | 2025-12-27 03:26:15 | MASTER-OAFA | (08h 24m 37.99s , +02d 59m 43.3s) | C | 60 | 19.3 | 6270 | 2025-12-27 03:27:20 | MASTER-OAFA | (08h 24m 37.98s , +02d 59m 45.5s) | C | 60 | 19.3 | 6335 | 2025-12-27 03:28:26 | MASTER-OAFA | (08h 24m 37.94s , +02d 59m 47.5s) | C | 60 | 19.3 | 6401 | 2025-12-27 03:29:31 | MASTER-OAFA | (08h 24m 37.94s , +02d 59m 49.7s) | C | 60 | 19.3 | 6466 | 2025-12-27 03:30:36 | MASTER-OAFA | (08h 24m 37.93s , +02d 59m 51.8s) | C | 60 | 19.3 | 6531 | 2025-12-27 03:31:42 | MASTER-OAFA | (08h 24m 37.90s , +02d 59m 53.7s) | C | 60 | 19.3 | 6597 | 2025-12-27 03:32:48 | MASTER-OAFA | (08h 24m 37.86s , +02d 59m 55.7s) | C | 60 | 19.3 | 6663 | 2025-12-27 03:33:53 | MASTER-OAFA | (08h 24m 37.82s , +02d 59m 57.5s) | C | 60 | 19.3 | 6728 | 2025-12-27 03:34:59 | MASTER-OAFA | (08h 24m 37.78s , +02d 59m 59.3s) | C | 60 | 19.3 | 6794 | 2025-12-27 03:36:05 | MASTER-OAFA | (08h 24m 37.74s , +03d 00m 01.2s) | C | 60 | 19.3 | 6859 | 2025-12-27 03:37:10 | MASTER-OAFA | (08h 24m 37.70s , +03d 00m 03.1s) | C | 60 | 19.3 | 6925 | 2025-12-27 03:38:15 | MASTER-OAFA | (08h 24m 37.65s , +03d 00m 04.7s) | C | 60 | 19.4 | 6991 | 2025-12-27 03:39:21 | MASTER-OAFA | (08h 24m 37.61s , +03d 00m 06.5s) | C | 60 | 19.4 | 7056 | 2025-12-27 03:40:27 | MASTER-OAFA | (08h 24m 37.56s , +03d 00m 07.9s) | C | 60 | 19.4 | 7122 | 2025-12-27 03:41:33 | MASTER-OAFA | (08h 24m 37.53s , +03d 00m 09.5s) | C | 60 | 19.3 | 7188 | 2025-12-27 03:42:39 | MASTER-OAFA | (08h 24m 37.47s , +03d 00m 10.9s) | C | 60 | 19.3 | 7254 | 2025-12-27 03:43:44 | MASTER-OAFA | (08h 24m 37.42s , +03d 00m 12.3s) | C | 60 | 19.3 | 7320 | 2025-12-27 03:44:50 | MASTER-OAFA | (08h 24m 37.37s , +03d 00m 13.7s) | C | 60 | 19.3 | 7442 | 2025-12-27 03:46:53 | MASTER-OAFA | (08h 24m 37.49s , +03d 02m 16.4s) | C | 60 | 18.5 | 7508 | 2025-12-27 03:47:58 | MASTER-OAFA | (08h 24m 37.46s , +03d 02m 17.6s) | C | 60 | 19.4 | 7573 | 2025-12-27 03:49:04 | MASTER-OAFA | (08h 24m 37.40s , +03d 02m 18.7s) | C | 60 | 19.3 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43243. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41331] IceCube-251225A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 27 Dec '25

27 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43242 SUBJECT: IceCube-251225A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/12/27 03:54:10 GMT FROM: Yuhua Yao at IceCube/UW-Madison <yyao255(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-251225A (https://gcn.nasa.gov/circulars/43239) in a time range of 1000 seconds centered on the alert event time (2025-12-25 20:05:46.800 UTC to 2025-12-25 20:22:26.800 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-251225A. We report a p-value of 1.00 in this time window. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.4e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-251225A in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 2e+02 GeV and 8e+04 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2025-12-24 20:14:06.800 UTC to 2025-12-26 20:14:06.800 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.7e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-251225A in a 2 day time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/43242. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41330] The EP-WXT trigger 01709250617 is likely a flaring star
by GCN Circulars 26 Dec '25

26 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43241 SUBJECT: The EP-WXT trigger 01709250617 is likely a flaring star DATE: 25/12/26 03:59:58 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C. Wang (IHEP, CAS), J. P. Feng, B. Zhang (USTC), T. Wu, H. C. Ding (AHNU), W. J. Zhang, H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709250617 at the time of 2025-12-26T02:55:13, is likely a stellar flare associated with G 177-25. The estimated flux of the flare is around 1.0×10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 1.8×10^30 erg/s. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/43241. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41329] IceCube Alert 251225.84: Global MASTER-Net observations report
by GCN Circulars 26 Dec '25

26 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43240 SUBJECT: IceCube Alert 251225.84: Global MASTER-Net observations report DATE: 25/12/26 00:39:34 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Tunka robotic telescope [1] located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the IceCube Alert 251225.84 (trigger No 19814286,19h 49m 58.80s , +22d 27m 50.4s, R=0.51) errorbox 12800 sec after notice time and 12867 sec after trigger time at 2025-12-25 23:48:34 UT, with upper limit up to 15.5 mag. Observations started at twilight. The observations began at zenith distance = 80 deg. The sun altitude is -11.8 deg. The galactic latitude b = -2 deg., longitude l = 60 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3085150 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 12873 | 2025-12-25 23:48:34 | MASTER-Tunka | (19h 49m 23.32s , +22d 04m 38.1s) | C | 10 | 15.4 | 12873 | 2025-12-25 23:48:34 | MASTER-Tunka | (19h 49m 40.90s , +21d 58m 08.5s) | C | 10 | 14.5 | 12896 | 2025-12-25 23:48:57 | MASTER-Tunka | (19h 49m 29.45s , +22d 03m 37.1s) | C | 10 | 15.3 | 12896 | 2025-12-25 23:48:57 | MASTER-Tunka | (19h 49m 46.97s , +21d 57m 07.9s) | C | 10 | 14.6 | 12921 | 2025-12-25 23:49:23 | MASTER-Tunka | (19h 49m 23.66s , +22d 02m 37.8s) | C | 10 | 15.2 | 12921 | 2025-12-25 23:49:23 | MASTER-Tunka | (19h 49m 41.14s , +21d 56m 09.7s) | C | 10 | 14.5 | 12945 | 2025-12-25 23:49:46 | MASTER-Tunka | (19h 49m 28.63s , +22d 02m 56.0s) | C | 10 | 15.1 | 12945 | 2025-12-25 23:49:46 | MASTER-Tunka | (19h 49m 46.21s , +21d 56m 26.8s) | C | 10 | 14.5 | 12972 | 2025-12-25 23:50:13 | MASTER-Tunka | (19h 49m 26.49s , +22d 04m 32.3s) | C | 10 | 15.2 | 12972 | 2025-12-25 23:50:13 | MASTER-Tunka | (19h 49m 44.04s , +21d 58m 04.3s) | C | 10 | 14.5 | 12997 | 2025-12-25 23:50:39 | MASTER-Tunka | (19h 49m 26.25s , +22d 02m 54.0s) | C | 10 | 15.2 | 12997 | 2025-12-25 23:50:39 | MASTER-Tunka | (19h 49m 43.95s , +21d 56m 23.9s) | C | 10 | 14.6 | 13020 | 2025-12-25 23:51:03 | MASTER-Tunka | (19h 49m 28.47s , +22d 04m 31.8s) | C | 5 | 15.0 | 13025 | 2025-12-25 23:51:03 | MASTER-Tunka | (19h 49m 28.47s , +22d 04m 31.7s) | C | 15 | 15.5 | Coadd 13020 | 2025-12-25 23:51:03 | MASTER-Tunka | (19h 49m 46.18s , +21d 58m 01.8s) | C | 5 | 14.4 | 13042 | 2025-12-25 23:51:25 | MASTER-Tunka | (19h 49m 23.36s , +22d 03m 41.2s) | C | 5 | 14.9 | 13042 | 2025-12-25 23:51:25 | MASTER-Tunka | (19h 49m 42.53s , +21d 57m 20.8s) | C | 5 | 14.4 | 13062 | 2025-12-25 23:51:46 | MASTER-Tunka | (19h 49m 22.30s , +22d 04m 41.4s) | C | 5 | 14.9 | 13062 | 2025-12-25 23:51:46 | MASTER-Tunka | (19h 49m 39.99s , +21d 58m 14.0s) | C | 5 | 14.3 | 13080 | 2025-12-25 23:52:03 | MASTER-Tunka | (19h 49m 28.75s , +22d 03m 40.6s) | C | 5 | 14.9 | 13080 | 2025-12-25 23:52:03 | MASTER-Tunka | (19h 49m 46.63s , +21d 57m 10.8s) | C | 5 | 14.4 | 13101 | 2025-12-25 23:52:25 | MASTER-Tunka | (19h 49m 23.26s , +22d 02m 41.2s) | C | 5 | 15.0 | 13101 | 2025-12-25 23:52:25 | MASTER-Tunka | (19h 49m 41.16s , +21d 56m 11.7s) | C | 5 | 14.4 | 13247 | 2025-12-25 23:54:24 | MASTER-Tunka | (19h 49m 22.94s , +22d 04m 41.5s) | C | 60 | 15.5 | 13247 | 2025-12-25 23:54:24 | MASTER-Tunka | (19h 49m 41.00s , +21d 58m 11.0s) | C | 60 | 14.8 | Coadd Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43240. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41328] IceCube-251225A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 25 Dec '25

25 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43239 SUBJECT: IceCube-251225A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/12/25 22:27:35 GMT FROM: Giacomo Sommani at Ruhr-Universität Bochum <gsommani(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 25-12-25 at 20:14:06.80 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_BRONZE alert stream. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 1.0705 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/141764_19814286.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 25-12-25 Time: 20:14:06.80 UT RA: 297.42 (+0.54/-0.49 deg 90% PSF containment) J2000 Dec: 22.47 (+0.46/-0.48 deg 90% PSF containment) J2000 We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino. No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of the event. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/43239. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41327] Fermi Gamma-ray Burst Monitor trigger 788368008/251225630 is not a GRB
by GCN Circulars 25 Dec '25

25 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43238 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 788368008/251225630 is not a GRB DATE: 25/12/25 16:54:22 GMT FROM: Bagrat Mailyan at Florida Tech <mbagrat(a)gmail.com> B. Mailyan (Florida Tech) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 788368008/251225630 at 15:06:43.51 UT on 25 December 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to particle activity." View this GCN Circular online at https://gcn.nasa.gov/circulars/43238. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41326] GRB 251222A: NUTTelA-TAO Early Measurements
by GCN Circulars 25 Dec '25

25 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43237 SUBJECT: GRB 251222A: NUTTelA-TAO Early Measurements DATE: 25/12/25 13:23:54 GMT FROM: Zhanat Maksut at Nazarbayev University <zhanat.maksut(a)nu.edu.kz> Z. Maksut (NU), B. Grossan (UCB, NU), T. Komesh (NU), D. Berdikhan (NU), E. Abdikamalov (NU), M. Krugov (FAI), K. Baigarin (NU), M. Coughlin (UNM), P. Hello (IJCLAB), S. Antier (IJCLAB), and S. Karpov (FZU) on behalf of the GRANDMA/NUTTelA-TAO: The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) pointed at GRB 251222A on receipt of an automated SVOM/ECLAIRs position alert. Observations started at 17:07:10 UT on 2025-12-22, 84 s after the SVOM/ECLAIRs trigger (Yang et al., GCN 43188). We observe in Sloan g' and i' bands simultaneously with the Burst Simultaneous Three-Channel Imager (Grossan, Kumar & Smoot 2019, JHEA, 32, 14). A new optical counterpart reported previously (Palmerio et al., GCN 43189; An et. al, GCN 43194; Calapai et. al, GCN 43195; Durbak et. al, GCN 43197; Li et. al, GCN 43203; Saccardi et. al, GCN 43208; Gupta et. al, GCN 43207; Saccardi et. al, GCN 43204; Kumar et. al, GCN 43209; Pérez-Fournon et. al, GCN 43212; Gupta et al., GCN 43224; Globus et al., GCN 43225; Pankov et al., GCN 43226; Freeberg et al., GCN 43229) was detected. We observe a rapid decay during the first ∼100 s, followed by a gradual rise leading to the first bump at around 500 s. The light curve then exhibits a decay until ∼4000 s, after which it rises again, reaching a second bump at around 10 ks. The total duration of the observations was about 4.5 hours. We report the following preliminary, uncorrected, selected photometric values: tc-t0(s) t_exp i'(mag) err(mag) g’(mag) err(mag) -------- ------ ------- -------- 85.5 3.0 16.2 0.08 17.02 0.09 117 30.0 17.58 0.07 19.45 0.09 519 30.0 17.32 0.08 18.22 0.07 3161 180.0 19.3 0.09 19.95 0.08 tc-t0 = trigger time minus image center time. Calibration was done with 5 bright Pan-STARRS catalog stars (see Komesh, T. et al. 2023, MNRAS 520, 6104). We caution that these are preliminary results, without color or other corrections. This research has been funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP26103591). The NUTTelA-TAO Team acknowledges the support of the staff of the Assy-Turgen Astrophysical Observatory, Almaty, Kazakhstan, and the Fesenkov Astrophysical Institute, Almaty, Kazakhstan. GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/) View this GCN Circular online at https://gcn.nasa.gov/circulars/43237. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41325] GRB 251222A/EP251222b: Optical detection with Kinder observations
by GCN Circulars 25 Dec '25

25 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43236 SUBJECT: GRB 251222A/EP251222b: Optical detection with Kinder observations DATE: 25/12/25 09:54:37 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> M.-H. Lee, A. Aryan, T.-W. Chen, W.-J. Hou, H.-Y. Hsiao (all NCU), A. K. H. Kong (NTHU), J. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), Y.-H. Lee, A. Sankar.K, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, C.-S. Lin, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the GRB/fast X-ray transient GRB 251222A/EP251222ba (Fermi/GBM team, GCN#43186; Yang et al., GCN#43188; Guo et al., GCN#43201; Shi et al., GCN#43215; Neights et al., GCN#43222) using the 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first SLT epoch of observations started at 10:39 UTC on the 23rd of December 2025 (MJD 61032.444), 17.55 hr after the Fermi/GBM detection. We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. In the stacked image, we clearly detected the optical counterpart candidate proposed by Palmerio et al. (GCN#43189) at a spectroscopic redshift of z = 3.171 (Saccardi et al., GCN#43204). The optical counterpart candidate was confirmed by several observations, including An et al. (GCN#43194); Calapai et al. (GCN#43195); Durbak et al. (NIR detection, GCN#43197); Li et al. (optical rebrightening, GCN#43203); Gupta et al. (GCN#43207, GCN#43224); Saccardi et al. (GCN#43208); Kumar et al. (GCN#43209); Pérez-Fournon et al. (GCN#43212); Globus et al. (GCN#43225); Pankov et al. (GCN#43226); Freeberg et al. (GCN#43229); Volnova et al. (GCN#43230) and Busmann et al. (GCN#43233). Moreover, we further utilized AutoPhOT to perform the PSF photometry. The details of the observations and the measured magnitude (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude. | avg. Seeing | med. Airmass SLT | i | 61032.444 | 17.55 | 300 * 12 | 19.48 +/- 0.07 | 3".7 | 2.27 The BALROG localization of the transient was reported by Preis et al. (GCN#43190), the Swift/XRT counterpart candidate was reported by Beardmore et al. (GCN#43213), and Frederiks et al. (GCN#43214) reported the Konus-Wind detection. The presented magnitude is calibrated using the field stars from the ATLAS-RefCat2 catalog from MAST (Tonry et al., 2018, ApJ, 867, 105) and is not corrected for the expected Galactic foreground extinction of A_i = 0.17 mag in the direction of the transient (Schlafly & Finkbeiner, 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al., 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/43236. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41324] EP251222a: Optical upper limit with Kinder observations
by GCN Circulars 25 Dec '25

25 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43235 SUBJECT: EP251222a: Optical upper limit with Kinder observations DATE: 25/12/25 09:50:48 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> M.-H. Lee, A. Aryan, T.-W. Chen, W.-J. Hou, H.-Y. Hsiao (all NCU), A. K. H. Kong (NTHU), J. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), Y.-H. Lee, A. Sankar.K, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, C.-S. Lin, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP251222a (Huang et al., GCN#43200; Guo et al., GCN#43216) using the 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first SLT epoch of observations started at 11:44 UTC on the 23rd of December 2025 (MJD 61032.489), 20.43 hr after the EP-WXT trigger. We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. Moreover, we utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al., 2019, AJ 157, 168) DR10 image using the 'sfft' (Hu et al., 2022, ApJ, 936, 157) algorithm. In the difference image, we did not detect the optical counterpart candidate (Li et al., GCN#43205; Malesani et al., GCN#43211; Busmann et al., GCN#43232) proposed at a redshift of z = 0.505 (An et al., GCN#43227). Moreover, we further utilized AutoPhOT to perform the PSF photometry. The details of the observations and the measured 3-sigma upper limit (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass SLT | i | 61032.489 | 20.43 | 300 * 24 | >21.4 | 2".8 | 1.16 The non-detection in our observations can be attributed to the relatively shallow limit and late follow-up. Our non-detection is consistent with Kumar et al. (GCN#43210) and Lipunov et al. (GCN#43219). The presented upper limit is calibrated using the field stars from the ATLAS-RefCat2 catalog from MAST (Tonry et al., 2018, ApJ, 867, 105) and is not corrected for the expected Galactic foreground extinction of A_i = 0.23 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al., 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/43235. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41323] GRB 251221A: Swift-BAT refined analysis
by GCN Circulars 25 Dec '25

25 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43234 SUBJECT: GRB 251221A: Swift-BAT refined analysis DATE: 25/12/25 05:09:07 GMT FROM: Mike Moss at NASA GSFC <mikejmoss3(a)gmail.com> A. Y. Lien (U Tampa), E. Ambrosi (INAF-IASFPA), S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 251221A (trigger #1426088) (Ambrosi, et al., GCN Circ. 43166). The BAT ground-calculated position is RA, Dec = 101.422, 0.738 deg which is RA(J2000) = 06h 45m 41.4s Dec(J2000) = +00d 44' 15.8" with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 42%. The mask-weighted light curves displays a complicated multi-pulsed light curve. The T90 (15-350 keV) is 56.86 +- 7.05 sec (estimated error including systematics). The time-averaged spectrum from T-38.10 to T+27.74 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.25 +- 0.13. The fluence in the 15-150 keV band is 2.0 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+2.91 sec in the 15-150 keV band is 1.1 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1426088 View this GCN Circular online at https://gcn.nasa.gov/circulars/43234. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41322] GRB 251222A/EP251222b: FTW optical and NIR observations
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43233 SUBJECT: GRB 251222A/EP251222b: FTW optical and NIR observations DATE: 25/12/24 14:24:34 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Xander J. Hall (CMU), Mitra Maleki (LMU), Brendan O'Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report: We observed the counterpart of GRB 251222A/EP251222b (Fermi GBM team et al. GCN 43186, Yang et al. GCN 43188, Palmerio et al. GCN 43189, Guo et al. GCN 43201, Huang et al. GCN 43215) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J-band simultaneously for 5 x 180 s starting at 2025-12-23T22:12:24 UT (1.21 days after the trigger). We detect the counterpart in all bands and measure an r-band magnitude of r = 20.68 +/- 0.02 AB mag. Our measurements are consistent with the reports by Lupinov et al. (GCN 43187), Palmerio et al. (GCN 43189), An et al. (GCN 43194), Calapai et al. (GCN 43195), Durbak et al. (GCN 43197), Li et al. (GCN 43203), Saccardi et al. (GCN 43204), Gupta et al. (GCN 43207), Saccardi et al. (CGN 43208), Kumar et al. (GCN 43209), Pérez-Fournon et al. (GCN 43212) Gupta et al. (GCN 43224), Glubus et al. (GCN 43225), Pankov et al. (GCN 43226), Freeberg et al. (GCN43229), and Volnova et al. (GCN 43230). The magnitude is calibrated against the PS1 catalog and not corrected for Galactic extinction. We thank Michael Schmidt from the Wendelstein Observatory for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/43233. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41321] EP251222a: FTW optical and NIR observations
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43232 SUBJECT: EP251222a: FTW optical and NIR observations DATE: 25/12/24 14:24:05 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Xander J. Hall (CMU), Mitra Maleki (LMU), Brendan O'Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report: We observed the counterpart of EP251222a (Huang et al. GCN 43200, Li et al. GCN 43205, Guo et al. GCN 43216) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J-band simultaneously for 10 x 180 s starting at 2025-12-23T21:27:09 UT (1.26 days after the trigger). We detect the counterpart in all bands. Using a template from the DESI Legacy Surveys, we measure an r-band magnitude of r = 21.64 +/- 0.06 AB mag. Our measurements are consistent with the reports by Li et al. (GCN 43205), Kumar et al. (GCN 43210), Malesani et al. (GCN 43211), and Lipunov et al. (GCN 43219). The magnitude is calibrated against the PS1 catalog and not corrected for Galactic extinction. We thank Michael Schmidt from the Wendelstein Observatory for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/43232. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41320] GRB 251205A: Kilonova-Catcher optical afterglow detection
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43231 SUBJECT: GRB 251205A: Kilonova-Catcher optical afterglow detection DATE: 25/12/24 12:30:36 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (OCA/IJCLab), M. Coughlin (UMN), S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 251205A detected by Swift/BAT (Lanava et al., GCN 43005), Fermi/GBM (Fermi GBM team, GCN 43059) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the TEC160FL telescope operated by M. Freeberg. Our observations started at TGRB+10.6h and were taken with sdss r and i filters. In our stacked frames, subtracted from the Pan STARRS DR2 template image, we detect the optical counterpart reported by Swift/UVOT (Lanava et al., GCN 43005, Klingler et al., GCN 43016), MASTER (Lipunov et al., GCN 43006), GTC/OSIRIS (de Ugarte Postigo et al., GCN 43008), NOT (Malesani et al., GCN 43009), GOTO (O'Neill et al., GCN 43010), COLIBRÍ (Mandarakas et al., GCN 43011) and Zeiss-1000 Koshka observatory (Pankov et al., GCN 43012), Liverpool telescope (Bochenek et al., GCN 43015, GCN 43024, GCN 43038), GROWTH (Patil et al., GCN 43019), ZTF and ATLAS (Pérez-Fournon et al., GCN 43020), FTW (Busmann et al., GCN 43026), MITSuME (Hagio et al., GCN 43029), WINTER (Mo et al., GCN 43044), 1.3m DFOT (Gupta et al., GCN 43067). We report our follow-up results in the table below: +---------------+-----------+------------+----------------+--------------+ | Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument | +===============+===========+============+================+==============+ | 10.86 | 10 x 180s | sdssr (AB) | 18.35 +/- 0.09 | TEC160FL | | 12.51 | 22 x 180s | sdssi (AB) | 18.56 +/- 0.09 | TEC160FL | | 35.63 | 20 x 180s | sdssr (AB) | 19.79 +/- 0.15 | TEC160FL | | 36.72 | 19 x 180s | sdssi (AB) | 19.91 +/- 0.30 | TEC160FL | +---------------+-----------+------------+----------------+--------------+ All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the sloan filters were calibrated using the PanSTARRS DR1 catalog. We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/) View this GCN Circular online at https://gcn.nasa.gov/circulars/43231. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41319] GRB 251222A: AbAO optical observations
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43230 SUBJECT: GRB 251222A: AbAO optical observations DATE: 25/12/24 11:20:29 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. A. Volnova (IKI), R. Ya. Inasaridze (AbAO), N. S. Pankov (HSE, IKI), A. S. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We observed the field of GRB 251222A (The Fermi GBM team, GCN 43186; Yang et. al, GCN 43188; Preis & Greiner, GCN 43190; Evans, GCN 43191; Beardmore et. al, GCN 43213; Frederiks et. al, GCN 43214; Guo et. al, GCN 43218; Neights et. al, GCN 43222) at z = 3.171 (Saccardi et. al, GCN 43204) with the AS-32 0.7m telescope of Abastumani Observatory (AbAO) taking several 60-second frames in R-band. The observations started on Dec. 23 at UT 18:16:00, i.e., ~ 1 day after the trigger. In the stacked image we detect the optical counterpart reported previously (Palmerio et. al, GCN 43189; An et. al, GCN 43194; Calapai et. al, GCN 43195; Durbak et. al, GCN 43197; Li et. al, GCN 43203; Saccardi et. al, GCN 43208; Gupta et. al, GCN 43207; Saccardi et. al, GCN 43204; Kumar et. al, GCN 43209; Pérez-Fournon et. al, GCN 43212; Gupta et al., GCN 43224; Globus et al., GCN 43225; Pankov et al., GCN 43226; Freeberg et al., GCN 43229). Preliminary photometry and observational details are the following: Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope (mid,days) (n*s) (3sigma) 2025-12-23 18:16:00 1.07935 72*60 R 20.46 0.18 21.3 AbAO/AS-32 The photometry is based on several nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43230. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41318] GRB 251222A / EP251222b: Kilonova-Catcher optical afterglow detection
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43229 SUBJECT: GRB 251222A / EP251222b: Kilonova-Catcher optical afterglow detection DATE: 25/12/24 11:03:12 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (OCA/IJCLab), M. Coughlin (UMN), S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 251222A / EP251222b detected by Fermi/GBM (Fermi GBM team, GCN 43186), SVOM (Yang et al., GCN 43188; Wang et al. GCN 43202), Einstein Probe (Guo et al., GCN 43201), Konus-WIND (Frederiks et al. GCN 43214) and Gecam-B (Guo et al., GCN 43218) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the iTelescope 72 located in Chile and the TEC160FL telescope operated by M. Freeberg. Our observations started at TGRB+7.9h and were taken with Rc and sdss r and i filters. In our stacked frames, subtracted from the Pan STARRS DR2 template image, we detect the optical counterpart reported by SVOM/VT (Palmerio et al., GCN 43189, Li et al., GCN 43203), NOT (An et al., GCN 43194), Calapai Astronomical Observatory (Calapai et al., GCN 43195), PRIME (Durbak et al., GCN 43197), VLT/Xshooter (Saccardi et al., GCN 43204), DFOT (Gupta et al., GCN 43207, GCN 43224), LCO/1m (Saccardi et al., GCN 43208; Pérez-Fournon et al., GCN 43212), GOTO (Kumar et al., GCN 43209), SVOM/COLIBRÍ (FM-GFT) (Globus et al., GCN 43225) and ZTSH (Pankov et al., GCN 43226). We report our follow-up results in the table below: +---------------+-----------+------------+----------------+-------------+ | Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument | +===============+===========+============+================+=============+ | 8.36 | 9 x 300s | Rc (Vega) | 19.28 +/- 0.03 | iT72 | | 9.95 | 15 x 180s | sdssr (AB) | 19.55 +/- 0.10 | TEC160FL | | 10.77 | 15 x 180s | sdssi (AB) | 19.45 +/- 0.17 | TEC160FL | | 32.8 | 12 x 300s | Rc (Vega) | 20.71 +/- 0.08 | iT72 | +---------------+-----------+------------+----------------+-------------+ All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the sloan filters were calibrated using the PanSTARRS DR1 catalog. Images obtained with the Johnson-Cousins filters were calibrated using the GAIA DR3 Synphot catalog. We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/) View this GCN Circular online at https://gcn.nasa.gov/circulars/43229. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41317] GRB 251129A / EP251129a: VLA detection of a radio counterpart
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43228 SUBJECT: GRB 251129A / EP251129a: VLA detection of a radio counterpart DATE: 25/12/24 10:46:36 GMT FROM: Tao An at SHAO, CAS <antao(a)shao.ac.cn> Tao An (SHAO), Ailing Wang (IHEP), Zigao Dai (USTC), and collaborators report on VLA observations of GRB 251129A. We observed GRB 251129A, also reported as EP251129a (e.g., GCNs 42877, 42879, 42880, 42882, 42884, 42887, 42888, 42891, 42897, 42900, 42902, 42959, 42972, 42985), with the Karl G. Jansky Very Large Array (VLA) under program VLA/25B-403 (AA627) on 2025 December 15 UT, approximately 16.0 days after the burst (relative to the SVOM/ECLAIRs trigger at 2025 Nov 29 02:32:05 UT). Observations were obtained in C band (4–8 GHz). A significant radio source is detected at the GRB position. Using standard wideband imaging, we measure: - Position (J2000): RA = 14:57:18.867 ± 0.044 s Dec = +79:17:34.74 ± 0.09″ - Peak flux density: 75.1 ± 8.4 μJy beam⁻¹ at 5 GHz 62.2 ± 9.4 μJy beam⁻¹ at 7 GHz The implied in-band spectral index across 5–7 GHz is consistent with being flat within uncertainties. The VLA position is consistent with the reported optical afterglow position (e.g., GCN 42883) and is also consistent with the X-ray localizations reported by SVOM/MXT, Swift/XRT, and Einstein Probe (e.g., GCN 42877, 42884, 42891), supporting the association of this radio source with GRB 251129A. This VLA detection provides an important radio counterpart to the unusual multi-wavelength behaviour of GRB 251129A reported in earlier GCNs, including its ultra-long high-energy emission and peculiar X-ray temporal and spectral evolution. We note that our eMERLIN observations reported in GCN 43040 resulted in a non-detection at C band between 2025 December 3-5, placing a 3σ upper limit of 0.066 mJy beam⁻¹ on the flux density. The new VLA detection therefore indicates a rising or previously sub-threshold radio afterglow component emerging on week timescales. More radio observations are encouraged to measure the temporal decay and spectral evolution and to distinguish between internal-engine and external-shock interpretations of this event. We thank the VLA Time Allocation Committee for approving these observations and the NRAO VLA operations and scheduling teams for the rapid execution and support that made this time-critical observation possible. View this GCN Circular online at https://gcn.nasa.gov/circulars/43228. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41316] EP251222a: VLT/FORS2 spectroscopic redshift z = 0.505
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43227 SUBJECT: EP251222a: VLT/FORS2 spectroscopic redshift z = 0.505 DATE: 25/12/24 09:47:04 GMT FROM: Laura Cotter at University College Dublin <laura.cotter(a)ucdconnect.ie> J. An (NAOC), L. Izzo (INAF/OACn & DARK/NBI), A. Saccardi (CEA/Irfu), L. Cotter (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), A. L. Thakur (INAF-IAPS), D. Xu (NAOC), report on behalf of the Stargate collaboration: We observed the optical counterpart (Li et al., GCN 43205; Malesani et al., GCN 43211) of EP251222a (Huang et al., GCN 43200; Guo et al., GCN 43216) with the ESO VLT UT1 (Antu) equipped with the FORS2 spectrograph. Our observations began on 2025 December 24 at 02:21:56 UT, 1.46 days post trigger. A spectrum covering the wavelength range 3600-8600 AA was secured using grism 300V (with no order-sorting filter), with a total exposure time of 4x600 s. In a preliminary reduction of the spectra, we detect a continuum over the entire wavelength range. From the detection of multiple absorption lines, which we interpret as the Mg II doublet (2796, 2804) and Fe II (2587, 2600), we infer a redshift of z = 0.505. At a consistent redshift, we also detect emission lines due to the [O II] 3726,3729 doublet and [O III] 5007 from the host galaxy. We acknowledge expert support from the observing staff in Paranal, in particular Elyar Sedaghati. View this GCN Circular online at https://gcn.nasa.gov/circulars/43227. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41315] GRB 251222A: ZTSH BVRI optical observations
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43226 SUBJECT: GRB 251222A: ZTSH BVRI optical observations DATE: 25/12/24 08:57:11 GMT FROM: Nicolai Pankov at IKI <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), V. Rumyantsev (CrAO), A. Pozanenko (IKI), A. Volnova (IKI) report on behalf of IKI-GRB-FuN: We performed optical observations of the field of GRB 251222A (The Fermi GBM team, GCN 43186; Yang et. al, GCN 43188; Preis & Greiner, GCN 43190; Evans, GCN 43191; Beardmore et. al, GCN 43213; Frederiks et. al, GCN 43214; Guo et. al, GCN 43218; Neights et. al, GCN 43222) at z = 3.171 (Saccardi et. al, GCN 43204) in the BVRI filters using the 2.6-meter ZTSh telescope of CrAO. The observations began in the I-filter on 2025-12-22 at 21:15 UT, i.e. 0.173 days since trigger. The optical counterpart (Palmerio et. al, GCN 43189; An et. al, GCN 43194; Calapai et. al, GCN 43195; Durbak et. al, GCN 43197; Li et. al, GCN 43203; Saccardi et. al, GCN 43208; Gupta et. al, GCN 43207; Saccardi et. al, GCN 43204; Kumar et. al, GCN 43209; Pérez-Fournon et. al, GCN 43212; Gupta et al., GCN 43224; Globus et al., GCN 43225) is detected in the majority of individual V,R images. The observation properties and the preliminary photometry of a V,R-filter image pair are presented in the table below: Date UT start t-T0 Exp. Filter OT Err. UL (mid, days) (s) (3sigma) 2025-12-22 21:36:41 0.188142 120 V 19.14 0.08 20.8 2025-12-22 21:38:48 0.189615 120 R 18.77 0.04 21.4 The photometry was calibrated using nearby stars from USNO-B1.0 and not corrected for the Galactic extinction. A power law fit to the R-filter light curve gives a temporal index of -0.64 +- 0.08. View this GCN Circular online at https://gcn.nasa.gov/circulars/43226. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41314] GRB 251222A: SVOM/COLIBRÍ (FM-GFT) optical observations
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43225 SUBJECT: GRB 251222A: SVOM/COLIBRÍ (FM-GFT) optical observations DATE: 25/12/24 08:20:51 GMT FROM: globus(a)astro.unam.mx Noémie Globus (UNAM), Camila Angulo (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Nikos Mandarakas (LAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and Hui Yang (IRAP) report: We imaged the field of GRB 251222A (Fermi GBM team, GCN Circ. 43186; Yang et al., GCN Circ. 43188; Guo et al., GCN Circ. 43201; Frederiks et al., GCN Circ. 43214; Guo et al. GCN Circ 43218) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-12-23 04:28 UTC to 08:22 UTC (from 11.37 to 15.27 hours after the trigger) and obtained 78 and 103 minutes of exposure in the r and z filters, respectively. We observed in poor weather conditions with variable transparency. The data were reduced, coadded, calibrated, and analyzed with the ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detected the optical counterpart discovered by Palmerio et al. (GCN Circ. 43189), and subsequently observed by An et al. (GCN Circ. 43194), Calapai (GCN Circ. 43195), Durbak et al. (GCN Circ, 43197), Li et al. (GCN Circ. 43203), Saccardi et al. (GCN Circ. 43204), Gupta et al. (GCN Cric. 43207), Saccardi et al. (GCN Circ. 43208), Kumar et al. (GCN Circ 43209), Pérez-Fournon et al. (GCN Circ. 43212) and Gupta et al. (GCN Circ. 43224), at preliminary magnitudes of: r = 19.83 +/- 0.01, z = 19.39 +/- 0.01. During our observations, the afterglow fades smoothly, with no evidence for further rebrightenings like the one reported by Li et al. (GCN Circ. 43203). We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/43225. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41313] GRB 251222A: Continued 1.3m DFOT optical observation
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43224 SUBJECT: GRB 251222A: Continued 1.3m DFOT optical observation DATE: 25/12/24 07:40:06 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180(a)gmail.com> Anshika Gupta, Kuntal Misra, Pankaj Pawar, Dhruv Jain, and Debalina Kar (ARIES) report: We observed the field of GRB 251222A detected by Fermi/GBM (Fermi GBM team, GCN 43186) and SVOM (Yang et al. 2025, GCN 43188) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on 2025-12-23 at 18:56:19 UT, i.e., ~ 25.84 hours after the Fermi/GBM trigger. We have taken multiple frames with an exposure time of 200s in the I filter. We stacked the images after the alignment. We detect an optical afterglow in our stacked image within the error box of SVOM (Palmerio et al. 2025, GCN 43189). We obtain the following preliminary magnitude in the stacked image: Date Start_UT T_start-T0 (hour) Filter Exp time (s) Magnitude =============================================================== 2025-12-23 18:56:19 ~25.84 I 200s*8 19.55 +/-0.02 The optical detection of the burst is consistent with Palmerio et al. 2025, (GCN 43189); An et al. 2025 (GCN 43194); Calapai et al. 2025 (GCN 43195); Durbak et al. 2025 (GCN 43197); Li et al. 2025 (GCN 43203); Saccardi et al. 2025 (GCN 43204); Gupta et al. 2025 (GCN 43207); Saccardi et al. 2025 (GCN 43208); Kumar et al. 2025 (GCN 43209); Pérez-Fournon et al. 2025 (GCN 43212). The magnitude is not corrected for the Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the USNO-B1.0 catalogue. View this GCN Circular online at https://gcn.nasa.gov/circulars/43224. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41312] EP251220a: 3.6m DOT optical afterglow detection
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43223 SUBJECT: EP251220a: 3.6m DOT optical afterglow detection DATE: 25/12/23 19:45:40 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180(a)gmail.com> Anshika Gupta, Kuntal Misra, Divyanshu Janghel, Debalina Kar, Dhruv Jain, and Pankaj Pawar (ARIES) report: We observed the field of EP251220a detected by EP/WXT (Liu et al. 2025; GCN 43162) with the 3.6m Devasthal Optical Telescope (DOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on 2025-12-21 at 17:13:18 UT, i.e., ~1.36 days after the EP/WXT trigger. We have taken multiple frames with an exposure time of 300s in the r filter. We stacked the images after the alignment. We detect a optical counterpart in our stacked image within the error box of COLIBRÍ telescope (Sánchez Álvarez et al. 2025; GCN 43167). We obtain the following preliminary magnitude in the stacked image: Date Start_UT T_start-T0 (days) Filter Exp time (s) Magnitude ================================================================== 2025-12-21 17:13:18 ~1.36 r 300s*8 21.64 +/-0.02 Our detection is consistent with Lipunov et al. 2025 (GCN 43163); Sánchez Álvarez et al. 2025 (GCN 43167); Kumar et al. 2025 (GCN 43169); Rakotondrainibe et al. 2025 (GCN 43170); Busmann et al. 2025 (GCN 43181); van Hoof et al. 2025 (GCN 43182); An et al. 2025 (GCN 43184); Passaleva et al. 2025 (GCN 43185); Volnova et al. 2025 (GCN 43221). The magnitude is not corrected for the Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the PanSTARRS DR1 catalog. View this GCN Circular online at https://gcn.nasa.gov/circulars/43223. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41311] EP251220a: 3.6m DOT optical afterglow detection
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43223 SUBJECT: EP251220a: 3.6m DOT optical afterglow detection DATE: 25/12/23 19:45:40 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180(a)gmail.com> Anshika Gupta, Kuntal Misra, Divyanshu Janghel, Debalina Kar, Dhruv Jain, and Pankaj Pawar (ARIES) report: We observed the field of EP251220a detected by EP/WXT (Liu et al. 2025; GCN 43162) with the 3.6m Devasthal Optical Telescope (DOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on 2025-12-21 at 17:13:18 UT, i.e., ~1.36 days after the EP/WXT trigger. We have taken multiple frames with an exposure time of 300s in the r filter. We stacked the images after the alignment. We detect a optical counterpart in our stacked image within the error box of COLIBRÍ telescope (Sánchez Álvarez et al. 2025; GCN 43167). We obtain the following preliminary magnitude in the stacked image: Date Start_UT T_start-T0 (days) Filter Exp time (s) Magnitude ================================================================== 2025-12-21 17:13:18 ~1.36 r 300s*8 21.64 +/-0.02 Our detection is consistent with Lipunov et al. 2025 (GCN 43163); Sánchez Álvarez et al. 2025 (GCN 43167); Kumar et al. 2025 (GCN 43169); Rakotondrainibe et al. 2025 (GCN 43170); Busmann et al. 2025 (GCN 43181); van Hoof et al. 2025 (GCN 43182); An et al. 2025 (GCN 43184); Passaleva et al. 2025 (GCN 43185); Volnova et al. 2025 (GCN 43221). The magnitude is not corrected for the Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the PanSTARRS DR1 catalog. View this GCN Circular online at https://gcn.nasa.gov/circulars/43223. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41310] GRB 251222A: Fermi GBM Observation
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43222 SUBJECT: GRB 251222A: Fermi GBM Observation DATE: 25/12/23 18:39:59 GMT FROM: eliza.neights(a)gmail.com Eliza Neights (GWU, NASA GSFC) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 17:05:51.27 UT on 22 December 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251222A (trigger 788115956/251222712). which was also detected by SVOM ECLAIRs, GRM, and MXT (H. Yang et al. 2025, GCN 43188), SVOM VT (J. T. Palmerio et al. 2025, GCN 43189), NOT (J. An et al. 2025, GCN 43194), Calapai Observatory (G. Calapai et al. 2025, GCN 43195), PRIME (J. Durbak et al. 2025, GCN 43197), EP WXT (C.-L. Guo et al. 2025, GCN 43201), DFOT (A. Gupta et al. 2025, GCN 43207), LCO (A. Saccardi et al. 2025, GCN 43208; I. Pérez-Fournon et al. 2025, GCN 43212), GOTO (A. Kumar et al. 2025, GCN 43209), Swift XRT (A.P. Beardmore et al. 2025, GCN 43213), and Konus Wind (D. Frederiks et al. 2025, GCN 43214). The spectroscopic redshift of GRB 251222A is found to be 3.171 by VLT/X-shooter (A. Saccardi et al. 2025, GCN 43204). The Fermi GBM on-ground location is consistent with the position reported by other instruments. The angle from the Fermi LAT boresight is 83 degrees. The GBM light curve consists of multiple emission episodes with a duration (T90) of about 83 s (50-300 keV). The time-averaged spectrum from T0-2.2 to T0+91.7 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.26 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 118 +/- 1 keV. The event fluence (10-1000 keV) in this time interval is (1.09 +/- 0.02)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+54 s in the 10-1000 keV band is 9.5 +/- 0.3 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 64.9 +/- 0.8 keV, alpha = -0.84 +/- 0.01 and beta = -2.0 +/- 0.02. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/43222. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41309] EP251220a: CrAO ZTSh optical observations
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43221 SUBJECT: EP251220a: CrAO ZTSh optical observations DATE: 25/12/23 18:19:15 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. A. Volnova (IKI), V. V. Rumyantsev (CrAO), A. S. Pozanenko (IKI), N. S. Pankov (HSE, IKI) report on behalf of IKI-GRB-FuN: We observed the field of the fast X-ray transient EP251220a detected by EP/WXT (Liu et al., GCN 43162) with the ZTSh 2.6m telescope of CrAO taking several 120-second frames in R-band. The observations started on Dec. 22 at UT 20:32:36, i.e., ~ 2.5 days after the EP/WXT trigger. In the stacked image we detect the optical counterpart reported previously (Sánchez Álvarez et al., GCN 43167; Kumar et al., GCN 43169; Rakotondrainibe et al., GCN 43170; Busmann et al., GCN 43181; van Hoof et al., GCN 43182; An et al., GCN 43184; Passaleva et al., GCN 43185). Preliminary photometry and observational details are the following: Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope (mid,days) (n*s) (3sigma) 2025-12-22 20:32:36 2.51642 17*120 R 22.55 0.20 22.9 CrAO/ZTSh The photometry is based on several nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43221. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41308] EP251221a: PRIME upper limit
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43220 SUBJECT: EP251221a: PRIME upper limit DATE: 25/12/23 17:54:25 GMT FROM: N. Passaleva at Sapienza University of Rome <niccolo.passaleva(a)uniroma1.it> N. Passaleva (U Rome), O. Guiffreda (UMD), M. El Kabir (U Rome), J. Durbak (UMD), E. Troja (U Rome), A. S. Kutyrev (NASA/GSFC), S. B. Cenko (NASA/GSFC) We observed the field of the fast x-ray transient EP251221a detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Dai et al. GCN 43178) in J and H filters with PRIME. Observations started ~24h after the trigger. Using Two Micron All Sky Survey (2MASS) nearby stars for preliminary calibration we do not detect any uncatalogued source down to J>21 AB (3-sigma) not corrected for galactic extinction in the WXT error region. PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa at the South African Astronomical Observatory (SAAO) (Kutyrev et al. 2023, Yama et al. 2023, Durbak et al. 2024). We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/43220. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41307] EP251222a: Global MASTER-Net observations report
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43219 SUBJECT: EP251222a: Global MASTER-Net observations report DATE: 25/12/23 15:36:29 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Tunka robotic telescope [1] located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the EP251222a ( EP Team et al., GCN 43200) errorbox 25213 sec after notice time and 69548 sec after trigger time at 2025-12-23 10:37:14 UT, with upper limit up to 16.4 mag. Observations started at twilight. The observations began at zenith distance = 78 deg. The sun altitude is -13.8 deg. MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the EP251222a errorbox 39747 sec after notice time and 84082 sec after trigger time at 2025-12-23 14:39:28 UT, with upper limit up to 16.9 mag. Observations started at twilight. The observations began at zenith distance = 75 deg. The sun altitude is -10.5 deg. The galactic latitude b = -35 deg., longitude l = 194 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3081644 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 66002 | 2025-12-23 09:36:37 | MASTER- | (04h 15m 01.67s , -00d 43m 08.5s) | C | 180 | 16.3 | 69578 | 2025-12-23 10:37:14 | MASTER-Tunka | (04h 09m 44.57s , -01d 55m 17.1s) | C | 60 | 16.4 | 69578 | 2025-12-23 10:37:14 | MASTER-Tunka | (04h 09m 58.83s , -02d 01m 41.0s) | C | 60 | 16.1 | 69649 | 2025-12-23 10:38:24 | MASTER-Tunka | (04h 09m 58.86s , -02d 01m 41.4s) | C | 60 | 15.7 | 69649 | 2025-12-23 10:38:25 | MASTER-Tunka | (04h 09m 44.41s , -01d 55m 16.5s) | C | 60 | 16.1 | 84112 | 2025-12-23 14:39:28 | MASTER-Kislovodsk | (04h 07m 57.86s , -01d 42m 13.8s) | C | 60 | 16.9 | 84112 | 2025-12-23 14:39:28 | MASTER-Kislovodsk | (04h 07m 58.58s , -01d 19m 40.7s) | C | 60 | 15.8 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43219. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41306] GRB 251222A / EP251222b: GECAM-B observation
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43218 SUBJECT: GRB 251222A / EP251222b: GECAM-B observation DATE: 25/12/23 15:23:20 GMT FROM: guohx(a)ihep.ac.cn Hao-Xuan Guo, Chen-Wei Wang, Yue Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by a long burst GRB 251222A at 2025-12-22T17:05:52.000 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43186), SVOM (H. Yang et al., GCN #43188, Chen-Wei Wang et al., GCN #43202), Einstein Probe (C.-L. Guo et al., GCN #43201) and Konus-Wind (D. Frederiks et al., GCN #43214). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses main emission with a duration (T90) of 55.8 +1.4/-9.6 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb251222A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/43218. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41305] GRB 251222A / EP251222b: GECAM-B observation
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43218 SUBJECT: GRB 251222A / EP251222b: GECAM-B observation DATE: 25/12/23 15:23:20 GMT FROM: guohx(a)ihep.ac.cn Hao-Xuan Guo, Chen-Wei Wang, Yue Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by a long burst GRB 251222A at 2025-12-22T17:05:52.000 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43186), SVOM (H. Yang et al., GCN #43188, Chen-Wei Wang et al., GCN #43202), Einstein Probe (C.-L. Guo et al., GCN #43201) and Konus-Wind (D. Frederiks et al., GCN #43214). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses main emission with a duration (T90) of 55.8 +1.4/-9.6 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb251222A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/43218. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41304] EP251221a: Liverpool Telescope upper limits
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43217 SUBJECT: EP251221a: Liverpool Telescope upper limits DATE: 25/12/23 15:21:03 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek and D. A. Perley (LJMU) report: We observed the field of the fast X-ray transient EP251221a (Dai et al., GCN 43178) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 3x120s exposures in SDSS r and i filters starting at 2025-12-22 23:12:54 UT, approximately 25.6 hours after the trigger. We perform image subtraction of the stacked images against Pan-STARRS using PSF matching with the help of PSFEx. We do not detect any new objects within the EP/WXT error region of the transient (Dai et al., GCN 43178). We note the i-band Pan-STARRS reference image is affected by a small number of artefacts, covering in total less than 1% of the error region. The 3-sigma limiting magnitudes on the stacked images are r > 22.6 and i > 22.5. View this GCN Circular online at https://gcn.nasa.gov/circulars/43217. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41303] EP251222a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43216 SUBJECT: EP251222a: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/12/23 14:23:50 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C.-L. Guo (NAO, CAS), R. Shi, Q.-J. Huang (PMO,CAS), X. Mao, and Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The X-ray transient EP251222a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Huang et al., GCN 43200), and followed by several telescopes (Li et al., GCN 43205, Kumar et al., GCN 43210, Malesani et al., GCN 43211). The refined analysis of the WXT data shows that this observation of the event started at T0=2025-12-22T14:59:14 (UTC). During the observation period of WXT (1100s), there was no significant short-timescale variability in the light curve. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 7.23 x 10^20 cm^-2 and a photon index of 1.58 (-0.4/+0.4). The derived average unabsorbed 0.5-4 keV flux is 6.35 (-4.9/+8.2) x 10^(-11) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously at 2025-12-22T15:21:49 (UTC), about 22 minutes after T0. The exposure time of this observation is 4081s. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 62.5014, DEC = -1.4795 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent positionally with the WXT transient. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 7.23 x 10^20 cm^-2 and a photon index of 2.34 (-0.05/+0.05). The derived average unabsorbed 0.5-10 keV flux is 7.54 (-5.2/+16.7) x 10^(-12) erg/s/cm^2. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/43216. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41302] EP251222b/GRB 251222A: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43215 SUBJECT: EP251222b/GRB 251222A: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/12/23 14:13:35 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.Shi, Q. J. Huang (PMO, CAS), C. L. Guo, X. Mao, Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP251222b triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Guo et al., GCN 43201), which is associated with GRB 251222A (Yang et al., GCN 43188), and followed by several telescopes (Palmerio et al., GCN 43189, Evans et al., GCN 43191, An et al., GCN 43194, Li et al., GCN 43203, Saccardi et al., GCN 43204, Gupta et al., GCN 43207, Saccardi et al., GCN 43208, Kumar et al., GCN 43209, Pérez-Fournon et al., GCN 43212, Beardmore et al., GCN 43213). The refined analysis of the WXT data shows that the event started at T0=2025-12-22T17:04:52 (UTC) and lasted for ~350 s with the peak flux of 1.4e-8 erg/s/cm^2. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 9.81e20 cm^-2 and a photon index of 1.1 (-/+0.15). The derived average unabsorbed 0.5-4 keV flux is 2.8 (-0.2/+0.3) x 10^(-9) erg/s/cm^2. The observation by the Follow-up X-ray Telescope (FXT) was performed at 2025-12-23T05:11:10 (UTC), about 12.11 hours after T0. The exposure time of this observation is 1884 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 77.1954, -7.2139 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 9.81e20 cm^-2 and a photon index of 1.86 (-0.25/+0.26). The derived average unabsorbed 0.5-10 keV flux is 1.8 (-0.3/+0.4) x 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Further observations are encouraged. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/43215. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41301] Konus-Wind detection of GRB 251222A / EP251222b
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43214 SUBJECT: Konus-Wind detection of GRB 251222A / EP251222b DATE: 25/12/23 12:47:21 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred(a)mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 251222A (Fermi-GBM detection: The Fermi GBM team, GCN 43186; SVOM detection: Yang et al., GCN 43188, Wang et al., GCN 43202), associated with the Einstein Probe X-ray transient EP251222b (Guo et al., GCN 43201), triggered Konus-Wind (KW) at T0=61605.670 s UT (17:06:45.670). The burst shows multiple emission pulses in the interval from T0-50 s to T0+33 s and has a total duration of ~83 s. The emission is seen up to ~2 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB251222_T61605/ As observed by Konus-Wind, the burst had the fluence of (9.92 ± 0.94)x10^-6 erg/cm^2 and the 64-ms peak energy flux, measured from T0 + 4.864 s, of (2.51 ± 0.32)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the brightest part of the burst (measured from T0 to T0+33.024 s) is best fit in the 20 keV - 15 MeV range by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.45 (-0.21, + 0.24) and Ep = 102(-16,+17) keV, chi^2 = 94/98 dof. The spectrum near the peak count rate (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 15 MeV range by a CPL model with alpha = -1.23 (-0.20, + 0.23)and Ep = 131(-14,+18) keV, chi^2 = 69/83 dof. Assuming the redshift z=3.121 (Saccardi et al., GCN 43204) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the burst isotropic energy release E_iso to (2.15 ± 0.20)x10^53 erg, the isotropic peak luminosity L_iso to (2.24 ± 0.28)x10^53 erg/s, the rest-frame peak energy of the time-integrated spectrum Ep,i,z to (420 ± 68) keV, and the rest-frame peak energy at the peak of the emission Ep,p,z to (540 ± 66) keV. With the obtained estimates, GRB 251222A is consistent with 68% prediction bands of both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB251222_T61605/GRB251222A_rest_frame.pdf All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/43214. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41300] Konus-Wind detection of GRB 251222A / EP251222b
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43214 SUBJECT: Konus-Wind detection of GRB 251222A / EP251222b DATE: 25/12/23 12:47:21 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred(a)mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 251222A (Fermi-GBM detection: The Fermi GBM team, GCN 43186; SVOM detection: Yang et al., GCN 43188, Wang et al., GCN 43202), associated with the Einstein Probe X-ray transient EP251222b (Guo et al., GCN 43201), triggered Konus-Wind (KW) at T0=61605.670 s UT (17:06:45.670). The burst shows multiple emission pulses in the interval from T0-50 s to T0+33 s and has a total duration of ~83 s. The emission is seen up to ~2 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB251222_T61605/ As observed by Konus-Wind, the burst had the fluence of (9.92 ± 0.94)x10^-6 erg/cm^2 and the 64-ms peak energy flux, measured from T0 + 4.864 s, of (2.51 ± 0.32)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the brightest part of the burst (measured from T0 to T0+33.024 s) is best fit in the 20 keV - 15 MeV range by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.45 (-0.21, + 0.24) and Ep = 102(-16,+17) keV, chi^2 = 94/98 dof. The spectrum near the peak count rate (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 15 MeV range by a CPL model with alpha = -1.23 (-0.20, + 0.23)and Ep = 131(-14,+18) keV, chi^2 = 69/83 dof. Assuming the redshift z=3.121 (Saccardi et al., GCN 43204) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the burst isotropic energy release E_iso to (2.15 ± 0.20)x10^53 erg, the isotropic peak luminosity L_iso to (2.24 ± 0.28)x10^53 erg/s, the rest-frame peak energy of the time-integrated spectrum Ep,i,z to (420 ± 68) keV, and the rest-frame peak energy at the peak of the emission Ep,p,z to (540 ± 66) keV. With the obtained estimates, GRB 251222A is consistent with 68% prediction bands of both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB251222_T61605/GRB251222A_rest_frame.pdf All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/43214. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41299] GRB 251222A: Swift-XRT afterglow detection
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43213 SUBJECT: GRB 251222A: Swift-XRT afterglow detection DATE: 25/12/23 11:12:39 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A.P. Beardmore (U. Leicester), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU), S. Lanava (PSU), J.P. Osborne (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected burst GRB 251222A. We searched for X-ray sources in 2.0 ks of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 2.0 ks, obtained between T0+10.7 ks and T0+17.4 ks. An uncatalogued X-ray source is detected within the estimated 3-sigma SVOM/ECLAIRs error region (49 arcsec) and is above the RASS 3-sigma upper limit at this position, and is therefore likely the GRB afterglow. Using 1130 s of PC mode data and 2 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 77.19502, -7.21354 which is equivalent to: RA (J2000): 05h 08m 46.81s Dec(J2000): -07d 12' 48.7" with an uncertainty of 2.5 arcsec (radius, 90% confidence). This position is 36 arcsec from the SVOM/ECLAIRs position. The light curve can be modelled with a power-law decay with a decay index of alpha=1.9 (+0.8, -0.7). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.92 (+0.31, -0.20). The best-fitting absorption column is 1.05 (+0.91, -0.12) x 10^21 cm^-2, consistent with the Galactic value of 9.3 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (4.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.05 (+0.91, -0.12) x 10^21 cm^-2 Galactic foreground: 9.3 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.92 (+0.31, -0.20) If the light curve continues to decay with a power-law decay index of 1.9, the count rate at T+24 hours will be 4.7 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x 10^-13 (2.0 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis of the likely afterglow are at https://www.swift.ac.uk/ToO_GRBs/00021895/Source1.php. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00021895. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/43213. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41298] GRB 251222A / EP251222b: LCO detection of the optical counterpart
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43212 SUBJECT: GRB 251222A / EP251222b: LCO detection of the optical counterpart DATE: 25/12/23 10:34:06 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon (IAC and ULL), F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia, E. Lekaroz-Urriza, M. Quintana-Ansaldo (all ULL), and A. López-Oramas (IAC and ULL) Following the detection of the long GRB 251222A / EP251222b detected by Fermi/GBM (The Fermi GBM team, GCN #43186; and Preis and Greiner, GCN #43190), SVOM ECLAIRs, GRM, and MXT (Yang et al., GCN #43188), EP/WXT (Guo et al., GCN #43201), SVOM/GRM (Wang et al., GCN 43202) and Swift-XRT (Evans, GCN #43191, source 1 of https://www.swift.ac.uk/ToO_GRBs/00021895/) we observed the field with one of the three Las Cumbres Observatory (LCO) 1-m telescopes equipped with Sinistro cameras located at the LCO node at Sutherland Observatory, South Africa. The observation, a single exposure of 300 sec in the SDSS r' filter, started on 2025-12-22 at 18:48:07 UT, about 1.7 hours after the SVOM and Fermi triggers. The optical counterpart detected by SVOM/VT (Palmerio et al., GCN #43189; and Li et al., GCN #43203) is clearly detected in our image with a magnitude of r' = 18.55 +/- 0.03 (AB), calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction. Our result is consistent with other optical and near-IR detections (Palmerio et al., GCN #43189; An et al., GCN #43194; Calapai et al., GCN #43195; Durbak et al., GCN #43197; Li et al., GCN #43203; Saccardi et al., GCN #43204; Gupta et al., GCN #43207; Saccardi et al., GCN #43208; and Kumar et al., GCN #43209). We notice a minimum in the light curve at the time of our LCO r'-band and the Calapai Observatory (Calapai et al., GCN #43195) observations. Saccardi et al. (GCN #43204) have reported a spectroscopic redshift of z = 3.171. This work makes use of observations from the Las Cumbres Observatory global telescope network (LCO program IAC2025B-008, SGLF and Superluminous Supernovae surveys). This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5). View this GCN Circular online at https://gcn.nasa.gov/circulars/43212. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41297] EP251222a: NTT/ULTRACAM optical observations
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43211 SUBJECT: EP251222a: NTT/ULTRACAM optical observations DATE: 25/12/23 08:11:19 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> D. B. Malesani (DAWN/NBI and Radboud), M. Stepney (CATA), D. Sahman (Sheffield), L. Cotter (UCD), G. Corcoran (UCD), P. G. Jonker (Radboud) report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP251222a (Huang et al., GCN 43200) using the ULTRACAM instrument on the ESO NTT telescope in La Silla (Chile). Observations consisted of 120 exposures by 15 s each, taken at a mean epoch 2025 December 23, 03:07:14 UT (11.81 hr after the EP trigger). The optical counterpart identified by Li et al. (GCN 43205) is well detected in our coadded image, for which we measure a magnitude r = 21.56 +- 0.08 (AB), calibrated against nearby stars from the Pan-STARRS catalog and not corrected for Galactic extinction. This confirms the rebrightening reported by Li et al. (GCN 43205). The consistency with the EP/FXT X-ray position (Huang et al., GCN 43200) makes this source the likely counterpart of EP251222a. Further follow-up is encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/43211. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41296] EP251222a: GOTO optical upper limit
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43210 SUBJECT: EP251222a: GOTO optical upper limit DATE: 25/12/23 08:03:47 GMT FROM: Amit Kumar at The Open University, UK <amitkundu515(a)gmail.com> A. Kumar, G. Ramsay, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, S. Belkin, D. O'Neill, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022; Dyer et al. 2024) in response to EP251222a (Huang et al., GCN 43200). Two sets of targeted observations were performed by GOTO-North at 2025-12-22 22:19:38 UT and 2025-12-23 01:14:12 UT, corresponding to 7.0 and 9.9 hours post-trigger, respectively. Each observation consisted of 4x90 s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogues. We do not identify any new optical source within the EP/WXT localisation uncertainty region after the trigger time, down to a 5-sigma limiting magnitude for the two sets of observations of L >20.4 (AB) and L >20.5 (AB). Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/43210. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41295] GRB 251222A / EP251222b: GOTO optical counterpart detection
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43209 SUBJECT: GRB 251222A / EP251222b: GOTO optical counterpart detection DATE: 25/12/23 07:19:23 GMT FROM: Amit Kumar at The Open University, UK <amitkundu515(a)gmail.com> A. Kumar, G. Ramsay, D. O’Neill, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) that serendipitously covered the field of GRB 251222A / EP251222b, detected by Fermi/GBM (The Fermi GBM team, GCN 43186), SVOM/ECLAIRs (Yang et al., GCN 43188), EP/WXT (Guo et al., GCN 43201) and SVOM/GRM (Wang et al., GCN 43202). Targeted observations were performed by GOTO-North at 2025-12-22 23:02:47 UT (5.95 hours post-trigger). The observation consisted of 4x45s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings. The optical afterglow (Palmerio et al., GCN 43189; An et al., GCN 43194; Calapai et al., GCN 43195; Durbak et al., GCN 43197; Li et al., GCN 43203; Saccardi et al., GCN 43204; Gupta et al., GCN 43207; Saccardi et al., GCN 43208) detected with an L-band magnitude of 19.51 ± 0.11 (AB). Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. Observations are ongoing. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/43209. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41294] GRB 251222A / EP251222b: LCO optical observations
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43208 SUBJECT: GRB 251222A / EP251222b: LCO optical observations DATE: 25/12/23 07:17:11 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi, J. T. Palmerio (CEA/Irfu), C. Wu, L.P. Xin (NAOC), H. Yang, S. Guillot (IRAP) report on behalf of the SVOM mission team: We observed the field of GRB 251222A (Yang et al., GCN 43188; Fermi GBM team, GCN 43186; Wang et al., GCN 43202; Guo et al., GCN 43201) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument. Our observation started at 2025-12-22T19:31:31 (about 2.43 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. The optical counterpart reported by Palmerio et al. (GCN 43189) is clearly detected in our images. We measure the following magnitudes, calibrated against the Pan-STARRS1 catalog, and not corrected for Galactic extinction: r = 18.29 +/- 0.01 AB (mid-time of 3.04 hr after the trigger); z = 18.17 +/- 0.01 AB (mid-time of 2.59 hr after the trigger). This result is consistent with the reports (An et al., GCN 43194; Durbak et al., GCN 43197, Li et al., GCN 43203). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/43208. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41293] GRB 251222A: 1.3m DFOT optical detection
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43207 SUBJECT: GRB 251222A: 1.3m DFOT optical detection DATE: 25/12/23 07:11:28 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180(a)gmail.com> Anshika Gupta, Kuntal Misra, Samrat Ghosh, Pankaj Pawar, Debalina Kar, and Dhruv Jain (ARIES) report: We observed the field of GRB 251222A detected by Fermi/GBM (Fermi GBM team, GCN 43186) and SVOM (Yang et al. 2025, GCN 43188) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on 2025-12-22 at 20:28:35 UT, i.e., ~ 3.38 hours after the Fermi/GBM trigger. We have taken multiple frames with an exposure time of 300s in the R filter. We stacked the images after the alignment. We detect an optical afterglow in our stacked image within the error box of SVOM (Palmerio et al. 2025, GCN 43189). We obtain the following preliminary magnitude in the stacked image: Date Start_UT T_start-T0 (hour) Filter Exp time (s) Magnitude =============================================================== 2025-12-22 20:28:35 ~3.38 R 300s*5 18.39 +/-0.01 The optical detection of the burst is consistent with Palmerio et al. 2025 (GCN 43189); An et al. 2025 (GCN 43194); Calapai et al. 2025 (GCN 43195); Durbak et al. 2025 (GCN 43197); Li et al. 2025 (GCN 43203); Saccardi et al. 2025 (GCN 43204). The magnitude is not corrected for the Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the USNO-B1.0 catalogue. View this GCN Circular online at https://gcn.nasa.gov/circulars/43207. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41292] GRB251221A: 7DT optical upper limits
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43206 SUBJECT: GRB251221A: 7DT optical upper limits DATE: 25/12/23 06:57:34 GMT FROM: Donggeun Tak <donggeun.tak(a)gmail.com> Donggeun Tak (SNU ARC/SNU), Myungshin Im (SNU ARC/SNU), YoungPyo Hong (SNU ARC/SNU), Hyeonho Choi (SNU ARC/SNU), Donghwan Hyun (SNU ARC/SNU), Gregory S.H. Paek (IfA, SNU ARC/SNU), Seo-Won Chang (SNU ARC/SNU), and Ji Hoon Kim (SNU ARC/SNU) report on behalf of the 7 Dimensional Telescope (7DT) team: We report optical follow-up observations of GRB251221A (Fermi/GBM GCN 43164; Swift GCN 43166) conducted with the 7-Dimensional Telescope (7DT), located in Chile. The 7DT follow-up observations began at 06:25:41 UTC on 2025-12-21, corresponding to approximately 1 hour after the trigger. The observations covered the target localization provided by Swift-XRT at RA, Dec = 101.42801 deg, 0.73241 deg, with an uncertainty radius of 2.1 arcseconds. Initial observations were carried out using 12 telescope units with 20 medium-band filters as well as g-, r-, i-band filters (23 filters in total). The following table summarizes (the observations and) the derived 5-sigma upper limits: Filter Mag Mag_err Exposure Date Time ---------------------------------------------------------------------------------------------------- g >20.32 N/A 600s 2025-12-21T06:27:52.833 r >19.54 N/A 600s 2025-12-21T06:34:05.833 i >18.54 N/A 600s 2025-12-21T06:27:56.167 m400 >18.61 N/A 600s 2025-12-21T06:34:09.167 m425 >19.09 N/A 600s 2025-12-21T06:34:04.667 m450 >19.23 N/A 600s 2025-12-21T06:27:50.667 m475 >19.21 N/A 600s 2025-12-21T06:34:05.167 m500 >19.36 N/A 600s 2025-12-21T06:27:57.333 m525 >19.05 N/A 600s 2025-12-21T06:34:08.167 m550 >18.66 N/A 600s 2025-12-21T06:34:12.833 m575 >18.94 N/A 600s 2025-12-21T06:28:00.500 m600 >18.88 N/A 600s 2025-12-21T06:27:58.500 m625 >18.48 N/A 600s 2025-12-21T06:34:30.000 m650 >18.42 N/A 600s 2025-12-21T06:27:52.667 m675 >18.35 N/A 600s 2025-12-21T06:34:26.333 m700 >18.40 N/A 600s 2025-12-21T06:27:55.000 m725 >17.92 N/A 600s 2025-12-21T06:34:13.500 m750 >17.75 N/A 1200s 2025-12-21T06:31:10.667 m775 >17.28 N/A 600s 2025-12-21T06:34:04.000 m800 >17.14 N/A 600s 2025-12-21T06:27:53.333 m825 >16.85 N/A 600s 2025-12-21T06:34:06.000 m850 >16.69 N/A 600s 2025-12-21T06:27:51.667 m875 >16.14 N/A 600s 2025-12-21T06:27:54.167 ---------------------------------------------------------------------------------------------------- No significant transient event was identified in the preliminary result. Preliminary analysis yields 5 sigma limiting magnitudes in the range of 16.14 – 20.32 mag depending on sky brightness and airmass. Photometric flux calibration was performed using synthetic photometry based on the Gaia DR3 XP catalog (Gaia Collaboration et al. 2022) within the AB magnitude system. Note that no extinction correction has been applied. The 7-Dimensional Telescope (7DT), located in Chile and comprising 20 wide-field telescopes equipped with 40 medium-bandwidth (~25nm) filters, aims to detect optical counterparts of GW sources and conduct the 7-Dimensional Sky Survey (7DS) of the Southern Hemisphere. Further information about the 7DT is available at http://7ds.snu.ac.kr/ and http://gwuniverse.snu.ac.kr/. View this GCN Circular online at https://gcn.nasa.gov/circulars/43206. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41291] EP251222a: GSP Optical Counterpart Detection
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43205 SUBJECT: EP251222a: GSP Optical Counterpart Detection DATE: 25/12/23 05:56:12 GMT FROM: Wenxiong Li at NAOC <liwenxiong1992(a)gmail.com> W. X. Li, S. J. Xue (NAOC); M. Andrews, J. Farah, D. A. Howell, C. McCully, and Kathryn Wynn (Las Cumbres Observatory), on behalf of a larger collaboration, report optical follow-up observations of EP251222a (Huang et al. GCN 43200) obtained with a Las Cumbres Observatory (LCO) 1-m telescope at at the Cerro Tololo Inter-American Observatory in Chile, ~12.5 hours after the EP-WXT trigger. We acquired 2 × 300 s exposures using the broad optical w band. Within the EP-FXT error region, we found that the source at R.A. = 62.5025, Dec. = –1.4792 brightened, increasing in brightness from r = 22.9 mag (DESI Legacy Survey) to r = 21.6 mag, with no other optical counterpart detected. These observations were taken as part of the Global Supernova Project (GSP). View this GCN Circular online at https://gcn.nasa.gov/circulars/43205. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41290] GRB 251222A / EP251222b: VLT/X-shooter spectroscopic redshift z = 3.171
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43204 SUBJECT: GRB 251222A / EP251222b: VLT/X-shooter spectroscopic redshift z = 3.171 DATE: 25/12/23 05:41:55 GMT FROM: Andrea Saccardi at CEA/Irfu <andrea.saccardi(a)cea.fr> A. Saccardi (CEA/Irfu), A. L. Thakur (INAF-IAPS), Z.P. Zhu, J. An (NAOC), D. B. Malesani (DAWN/NBI and Radboud), L. Cotter, A. Martin-Carrillo (UCD), report on behalf of the Stargate collaboration: We observed the optical/NIR counterpart (Palmerio et al., GCN 43189; An et al., GCN 43194; Calapai et al., GCN 43195; Durbak et al., GCN 43197; Li et al., GCN 43203) of the GRB 251222A / EP251222b detected by Fermi/GBM (Fermi GBM team, GCN 43186), SVOM/ECLAIRs (Yang et al., GCN 43188), EP/WXT (Guo et al., GCN 43201) and SVOM/GRM (Wang et al., GCN 43202) using the ESO/VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 AA and consist of 2 exposures of 600 s each. Observations started on 2025 December 23 at 03:38:43 UT (10.55 hr after the burst). In a 15-s acquisition image secured in the r band (10.45 hr after trigger), we measure r = 19.91 +/- 0.04 (AB), calibrated against nearby stars from Pan-STARRS. In a preliminary reduction of the spectra, we clearly detect a continuum over the entire wavelength range and a trough due to Lya absorption visible at ~5070 AA. From the detection of multiple absorption features, including S II, Si II, Si II*, O I, O I*, Ni II, Si IV, C IV, Fe II, Fe II*, Al II, Al III, Cr II, Ni II*, Mg II, and Mg I we infer a redshift of z = 3.171. At the same redshift we also detect absorption features consistent with Ly-beta, Ly-gamma, and the Lyman-limit. We acknowledge the excellent support of the ESO observing staff in Paranal. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495) View this GCN Circular online at https://gcn.nasa.gov/circulars/43204. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41289] GRB 251222A / EP251222b: SVOM/VT optical rebrightening
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43203 SUBJECT: GRB 251222A / EP251222b: SVOM/VT optical rebrightening DATE: 25/12/23 05:39:41 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, Y. N. Ma, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) , H. Yang, S. Guillot (IRAP) report on behalf of the SVOM/VT team. SVOM/VT performed an automatic slew on the burst GRB 251222A (SVOM trigger reference:sb25061207) triggered by SVOM/ECLAIRs (Zhang et al., GCN 40697) and also detected by SVOM/GRM (Wang et al., GCN 43202), and Fermi/GBM (Fermi GBM team, GCN 43186), which is likely associated with EP251202b (Guo et al., GCN 43201). The observation began at 2025-12-22T17:09:44 UTC, i.e. 238 seconds after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With the data received, the optical counterpart (Palmerio et al., GCN 43819; An et al., GCN 43194; Durbak et al., GCN 43197) was rising at early time to the peak of VT_R~17.37+/-0.02 mag at 389 sec and then fading in both channels with the slope of -0.92. At around 10000 seconds, the brightness was VT_R ~ 18.09+/-0.02 mag confirming a rebrightening between the epoch, and then decayed with the slope of -0.84. The result would be be refined with more data received. The measurements are derived in AB magnitude as follows: mid-time | exposure time | band | mag (AB) ------------|----------------- |------------------- 263 sec | 50 sec | VT_B | 18.27+/-0.03 263 sec | 50 sec | VT_R | 17.57+/-0.02 5.242 hour | 100 sec | VT_B | 19.28+/-0.04 5.242 hour | 100 sec | VT_R | 18.56+/-0.03 Our photometry was not corrected for Galactic extinction. More VT follow ups are scheduled. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/43203. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41288] EP251222b/GRB 251222A: SVOM/GRM observation
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43202 SUBJECT: EP251222b/GRB 251222A: SVOM/GRM observation DATE: 25/12/23 04:07:28 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Wen-Jun Tan, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Hui Yang (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 251222A (SVOM trigger reference: sb25122207) at 2025-12-22T17:05:52.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN#43186), SVOM/ECLAIRs (Yang et al., GCN#43188) and EP (Guo et al., GCN#43201). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 85.5 +3.0/-3.5 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251222A.png In addition, the position of this burst, as determined by SVOM/ECLAIRs (RA= 77.202 deg, DEC= -7.206 deg, ERR=29 arcsec), is located at about 34 degrees from the SVOM optical axis. With this localization, the time-averaged spectrum from T0-20 to T0+100 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.95 +0.10/-0.09 and the cutoff energy, parameterized as Epeak, is 453 +63/-50 keV. The event fluence (10-1000 keV) in this time interval is (1.37 +0.17/-0.14)E-05 erg/cm^2. The 1s peak spectrum, measured from T0+53 to T0+54 s, is also best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.95 +0.12/-0.12 and the cutoff energy, parameterized as Epeak, is 209 +40/-28 keV. The flux (10-1000 keV) in this time interval is (1.05 +0.09/-0.08)E-06 erg/cm^2/s. The localization of GRB 251222A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251222A_amati.png And the localization in the 'Yonetoku' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251222A_yonetoku.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/43202. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41287] EP251222b/GRB 251222A: Einstein Probe detection of an X-ray transient
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43201 SUBJECT: EP251222b/GRB 251222A: Einstein Probe detection of an X-ray transient DATE: 25/12/23 03:35:23 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C.-L. Guo (NAO, CAS), R. Shi (PMO, CAS), Q.-J. Huang (PMO,CAS), X. Mao (NAO, CAS), and Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP251222b. The transient triggered EP-WXT (ID: 01709250454) at 2025-12-22 17:05:34 (UTC). The WXT position of the source is R.A. = 77.207 deg, DEC = -7.208 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). EP251222b is located 0.8 arcmin away from GRB 251222A (GCN 43189), and the trigger time is differ by only 12 seconds. Thus EP251222b is possibly associated with GRB 251222A. Further information will be updated when the telemetry data are received. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/43201. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41286] EP251222a: Einstein Probe detection of an X-ray transient
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43200 SUBJECT: EP251222a: Einstein Probe detection of an X-ray transient DATE: 25/12/23 03:34:27 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. J. Huang, R. Shi (PMO, CAS), C. L. Guo (NAO, CAS), X. Mao (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP251222a. The transient triggered EP-WXT (ID: 01709250453) at 2025-12-22 15:18:06 (UTC). The WXT position of the source is R.A. = 62.519 deg, DEC = -1.506 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 62.5014 deg, DEC = -1.4795 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data are received. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/43200. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41285] The EP-WXT trigger 01709250397 is likely a flaring star
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43199 SUBJECT: The EP-WXT trigger 01709250397 is likely a flaring star DATE: 25/12/23 02:44:39 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.Shi, Q.J.Huang (PMO,CAS), C.L.Guo (NAO,CAS), X.Mao (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709250397 at the time of 2025-12-22 10:35:15, is likely a stellar flare associated with V* LL Eri. The estimated flux of the flare is around 1.2e-10 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 4.6e31 erg/s. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/43199. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41284] EP251221a: Global MASTER-Net observations report
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43198 SUBJECT: EP251221a: Global MASTER-Net observations report DATE: 25/12/23 02:27:30 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Tunka robotic telescope [1] located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the EP251221a ( EP Team et al., GCN 43178) errorbox 25137 sec after notice time and 48513 sec after trigger time at 2025-12-22 11:07:39 UT, with upper limit up to 14.1 mag. The observations began at zenith distance = 80 deg. The sun altitude is -18.4 deg. MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the EP251221a errorbox 77221 sec after notice time and 1 days 14196 sec after trigger time at 2025-12-23 01:35:42 UT, with upper limit up to 18.3 mag. The observations began at zenith distance = 48 deg. The sun altitude is -32.6 deg. The galactic latitude b = 12 deg., longitude l = 193 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3080482 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 48543 | 2025-12-22 11:07:39 | MASTER-Tunka | (06h 57m 20.46s , +23d 03m 38.7s) | C | 60 | 14.1 | 48543 | 2025-12-22 11:07:39 | MASTER-Tunka | (06h 57m 34.89s , +22d 56m 36.5s) | C | 60 | 13.3 | 52254 | 2025-12-22 12:08:30 | MASTER- | (07h 00m 06.39s , +23d 40m 37.8s) | C | 180 | 18.9 | 52254 | 2025-12-22 12:08:30 | MASTER- | (07h 00m 04.96s , +24d 36m 38.8s) | C | 180 | 18.4 | 100687 | 2025-12-23 01:35:42 | MASTER-Kislovodsk | (06h 57m 08.12s , +23d 26m 58.0s) | C | 180 | 18.2 | 100687 | 2025-12-23 01:35:42 | MASTER-Kislovodsk | (06h 56m 59.41s , +23d 49m 39.5s) | C | 180 | 18.3 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43198. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41283] GRB 251222A: PRIME near-infrared detection
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43197 SUBJECT: GRB 251222A: PRIME near-infrared detection DATE: 25/12/23 01:48:17 GMT FROM: Joe Durbak at UMD <gcn.joedurbak(a)gmail.com> J. Durbak (UMD), N. Passaleva (U Rome), O. Guiffreda (UMD), M. El Kabir (U Rome), E. Troja (U Rome), A. S. Kutyrev (NASA/GSFC), S. B. Cenko (NASA/GSFC) Following the Fermi GBM detection (GCN 43186) and SVOM (Yang et al., GCN 43188), we observed the transient field in Y, J and H filters with PRIME ~2 hours after Fermi and SVOM detections. At the position of the optical counterpart reported by SVOM/VT (Palmerio et al., GCN 43189), we detect an uncatalogued source in J band. Using nearby VISTA Hemispherical Survey (VHS) stars for preliminary calibration we derive the following magnitudes, not corrected for Galactic extinction: Filter | Mag(AB) | -------|----------------| J | 18.04 +/- 0.02 | Further observations are planned. PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa at the South African Astronomical Observatory (SAAO) (Kutyrev et al. 2023, Yama et al. 2023, Durbak et al. 2024, Sumi et al. 2025). We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/43197. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41282] GRB 251222A: PRIME near-infrared detection
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43197 SUBJECT: GRB 251222A: PRIME near-infrared detection DATE: 25/12/23 01:48:17 GMT FROM: Joe Durbak at UMD <gcn.joedurbak(a)gmail.com> J. Durbak (UMD), N. Passaleva (U Rome), O. Guiffreda (UMD), M. El Kabir (U Rome), E. Troja (U Rome), A. S. Kutyrev (NASA/GSFC), S. B. Cenko (NASA/GSFC) Following the Fermi GBM detection (GCN 43186) and SVOM (Yang et al., GCN 43188), we observed the transient field in Y, J and H filters with PRIME ~2 hours after Fermi and SVOM detections. At the position of the optical counterpart reported by SVOM/VT (Palmerio et al., GCN 43189), we detect an uncatalogued source in J band. Using nearby VISTA Hemispherical Survey (VHS) stars for preliminary calibration we derive the following magnitudes, not corrected for Galactic extinction: Filter | Mag(AB) | -------|----------------| J | 18.04 +/- 0.02 | Further observations are planned. PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa at the South African Astronomical Observatory (SAAO) (Kutyrev et al. 2023, Yama et al. 2023, Durbak et al. 2024, Sumi et al. 2025). We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/43197. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41281] EP251221a: NOT optical upper limit
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43196 SUBJECT: EP251221a: NOT optical upper limit DATE: 25/12/23 01:19:56 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L. B. He, J. An, X. Liu, D. Xu (NAOC), D. B. Malesani (DAWN/NBI and Radboud), J. A. Chacon (PUC), F. E. Bauer (SSI and UTA), P. G. Jonker (Radboud), A. Kadela (NOT and NBI), report on behalf of a larger collaboration: We observed the field of EP251221a (Dai et al., GCN 43178) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were obtained in the r and z band, starting on 2025-12-22 at 03:00:12 UTC (5.35 hr after the WXT trigger). No new optical source is detected within the EP/WXT error circle. And we obtained the following upper limits: | Band | t_mid - T0 (hr) | Exposure time | 5-sigma upper limit | |--|--|--|--| | r | 5.47 | 1x300s+1x180s | 23.5 | | r | 6.25 | 3x300s | 23.8 | | z | 7.21 | 5x200s | 22.3 | calibrated with nearby Pan-STARRS stars and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43196. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41280] GRB 251222A: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43195 SUBJECT: GRB 251222A: Calapai Observatory, Massa S. Giorgio (Messina), optical observation. DATE: 25/12/23 01:14:18 GMT FROM: Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, Messina, Italy <giovannicalapai(a)tiscali.it> Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, (Messina) Italy Member of: GRB/UAI Gamma Ray Burst Section of Unione Astrofili Italiani. Report: We observed the field of GRB 251222A detected by SVOM/ECLAIRs (Yang et al., GCN 43188) and Fermi Gamma-ray Burst Monitor (GCN 43186) with the 11 inches Schmidt-Cassegrain (Celestron 11) telescope F/D=6,3. The observations were started at 2025-12-22 18:27:54 UT (approximately 1.37 hours after burst) stacking a sets of unfiltered CCD image. The observations were carried out with clear skies, good visibility conditions and light gusts of wind. The OT was detected at the following position: RA (J2000.0) 05h 08m 46.7s Decl. (J2000.0) -07° 12' 48.4" Photometry was obtained using nearby PanSTARRS stars as follows: Observation Mid-Time T-T0 (hr) Exposure Filter Mag. Mag. err. 2025-12-22 18:56:55 UT 1.85 30x60s CR 18.70 +/- 0.09 Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. No correction for galactic dust extinction was applied. Our observations are consistent with other already reported Palmerio et al. (GCN 43189); An et al. (GCN 43194). The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/43195. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41279] GRB 251222A: NOT optical observations
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43194 SUBJECT: GRB 251222A: NOT optical observations DATE: 25/12/22 23:07:49 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> J. An (NAOC), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), B. Schneider (LAM), A. Saccardi (CEA/Irfu), L. Cotter (UCD), M. A. Diaz Teodori, A. Nitindala (University of Turku), report on behalf of a larger collaboration: We observed the optical counterpart (Palmerio et al., GCN 43189) of GRB 251222A (Yang et al., GCN 43188; Fermi GBM team, GCN 43186) using the Nordic Optical Telescope equipped with the Standby Camera (StanCam). A series of 3 x 300s exposures were taken in the R band starting at 2025-12-22T21:34:54. The afterglow is well detected in the individual images with an AB magnitude of R = 18.96 +/- 0.02 at a mid-time of 4.53 hr after the trigger. Our photometry was calibrated using nearby stars from the Pan-STARRS catalog and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43194. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41278] IceCube-251218A: No Candidate Transients from the Zwicky Transient Facility
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43193 SUBJECT: IceCube-251218A: No Candidate Transients from the Zwicky Transient Facility DATE: 25/12/22 21:43:04 GMT FROM: Jannis Necker at DESY <jannis.necker(a)desy.de> Jannis Necker (Leiden University), Akshay Eranhalodi (DESY), Robert Stein (JSI), and Anna Franckowiak (Ruhr University Bochum) report, On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: As part of the ZTF neutrino follow up program (Stein et al. 2023), we observed the localization region of the neutrino event IceCube-251218A (Zegarelli et. al, GCN 43151) with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the r-band beginning at 2025-12-19 04:45 UTC, approximately 8.4 hours after event time. We covered 100.0% (1.1 sq deg) of the reported localization region. This estimate accounts for chip gaps. The exposure was 300s with a typical depth of 21.0 mag. The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019) . No candidate counterparts were detected. This is consistent with previously reported upper limits (Antier et al. 2025, GCN 43153). Observations of this field will continue as part of our standard ToO cadence for high-energy neutrinos (Stein et al. 2023). ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA; WIS, Israel; OKC, Sweden; JSI/UMd, USA; DESY, Germany; TANGO, Taiwan; UW Milwaukee, USA; LANL, USA; TCD, Ireland; IN2P3, France. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert database searches are done by AMPEL (Nordin et al. 2019). Alert filtering is performed with the nuztf (Stein et al. 2021, https://github.com/desy-multimessenger/nuztf ). View this GCN Circular online at https://gcn.nasa.gov/circulars/43193. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41277] IPN triangulation of GRB 251220B (short)
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43192 SUBJECT: IPN triangulation of GRB 251220B (short) DATE: 25/12/22 21:25:26 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the HEND/Mars Odyssey team, A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, and T. Cline on behalf of the Konus-Wind team, A. Goldstein, M. S. Briggs, C. Wilson-Hodge, and E. Burns on behalf of the Fermi GBM team, S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, A. Tohuvavohu, and J. DeLaunay on behalf of the Swift-BAT team, and W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr, and A.S. Gardner on on behalf of the GRS-Odyssey GRB team, report: The short-duration GRB 251220B (Fermi/GBM detection: The Fermi GBM team, GCN 43160; SVOM/GRM observation: Wang et al., GCN 43171) was detected by Fermi(GBM trigger 787966689), Konus-Wind, Swift(BAT), SVOM (GRM), and Mars-Odyssey (HEND), at about 85085 s UT (23:38:05). The burst was outside the coded field of view of the BAT. We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 246.020 (16h 24m 05s) +44.550 (+44d 33' 00") Corners: 242.980 (16h 11m 55s) +43.398 (+43d 23' 51") 248.478 (16h 33m 55s) +45.405 (+45d 24' 19") 249.037 (16h 36m 09s) +45.540 (+45d 32' 24") 243.550 (16h 14m 12s) +43.587 (+43d 35' 13") --------------------------------------------- The error box area is 597 sq. arcmin, and its maximum dimension is 4.82 deg (the minimum one is 2.3 arcmin). The Sun distance was 71 deg. This localization may be improved. A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB251220_T85082/IPN/ The HEALPix triangulation map is the multi-order HEALPix in units of probability density. The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/43192. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41276] GRB 251222A: Swift ToO observations
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43191 SUBJECT: GRB 251222A: Swift ToO observations DATE: 25/12/22 20:09:26 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a ToO observation of the SVOM/ECLAIRs-detected event GRB 251222A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021895 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the SVOM/ECLAIRs event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration. Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/43191. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41275] GRB 251222A: BALROG localization (Fermi Trigger / GRB 251222712)
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43190 SUBJECT: GRB 251222A: BALROG localization (Fermi Trigger / GRB 251222712) DATE: 25/12/22 18:24:42 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger at 17:05:51 on 22 Dec. 2025 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 76.6 deg Decl.(2000.0) = -7.7 deg The 1 sigma statistical error radius is 2.5 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB251222712/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB251222712/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB251222712/json View this GCN Circular online at https://gcn.nasa.gov/circulars/43190. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41274] GRB 251222A: SVOM/VT optical candidate
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43189 SUBJECT: GRB 251222A: SVOM/VT optical candidate DATE: 25/12/22 17:48:55 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> J. T. Palmerio (CEA/Irfu), Y. L. Qiu, C. Wu, L. P. Xin (NAOC) on behalf of the SVOM/VT team. After the trigger by SVOM/ECLAIRs at 2025-12-22T17:05:46 UTC (T0), SVOM performed an automatic slew on the burst location (Yang et al., GCN 43188). SVOM/VT began observing the field at 2025-12-22T17:10:47, 300.27 seconds after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. From a preliminary analysis of the 1-bit subimage and source list downloaded via VHF network, at least one credible candidate is identified, the details of which are presented below. VT_ID 117: This bright candidate was flagged as an uncatalogued fading source. The position of this candidate is R.A., Dec. 77.1948558, -7.2135525 degrees, corresponding to: R.A. (J2000) = 05h08m46.8s Dec. (J2000) = -07d12m48.8s with an uncertainty of 0.5 arcsec. This location is within the R90 uncertainty region of the SVOM/MXT onboard localization. The source was detected in both VT_R and VT_B. The candidate's magnitudes are: | date-obs (UTC) | mid-time | exposure | band | mag(AB) | | -------------------- | ----------- | --------- | ----- | ------------- | | 2025-10-13T17:44:04 | 7.5 min | 6*50 sec | VT_B | 18.70 ± 0.01 | | 2025-10-13T17:44:04 | 7.5 min | 6*50 sec | VT_R | 17.89 ± 0.01 | Magnitudes were not corrected for dust extinction. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/43189. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41273] GRB 251222A: SVOM detection of a long burst
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43188 SUBJECT: GRB 251222A: SVOM detection of a long burst DATE: 25/12/22 17:37:38 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> H. Yang, S. Guillot (IRAP), D. Götz (CEA), Y. Huang (IHEP) report on behalf of the SVOM mission team: At 2025-12-22T17:05:46 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251222A (SVOM burst-id sb25122206). The burst was also detected by Fermi/GBM (GCN # 43186). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was only detected by the Count-Rate Trigger (CRT), which produced a sequence of 9 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 26.30 in the [8-50] keV energy band over a time window of 20.40 seconds starting at 2025-12-22T17:05:51. The localization of the best alert is R.A., Dec. 77.2146, -7.2161 degrees (J2000) with a 90% confidence level (C.L.) radius of 3.55 arcmin (including systematic error of 2 arcmin added in quadrature). This burst also triggered SVOM/GRM at 2025-12-22T17:05:52. SVOM slewed to the burst. SVOM/MXT began observing the field at 2025-12-22T17:08:42 UTC, 176 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 77.202, -7.206 degrees: R.A. (J2000) = 5h08m48.5s Dec. (J2000) = -7d12m21.6s with a 90% C.L. radius of 29 arcseconds (including systematics). This location is 1 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. VT began observing the field after the slew. The analysis of the data will be published in a future circular. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Hui Yang: hyang(a)irap.omp.eu. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/43188. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41272] SVOM GRB251222.71: Global MASTER-Net observations report
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43187 SUBJECT: SVOM GRB251222.71: Global MASTER-Net observations report DATE: 25/12/22 17:28:28 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Tunka robotic telescope [1] located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the SVOM GRB251222.71 (trigger No 1766423142,05h 08m 53.93s , -07d 11m 56.4s, R=0.0699) errorbox 607 sec after notice time and 841 sec after trigger time at 2025-12-22 17:19:43 UT, with upper limit up to 16.5 mag. The observations began at zenith distance = 60 deg. The sun altitude is -62.3 deg. The galactic latitude b = -25 deg., longitude l = 208 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3081133 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 872 | 2025-12-22 17:19:43 | MASTER-Tunka | (05h 08m 48.67s , -06d 53m 37.5s) | C | 60 | 16.5 | 872 | 2025-12-22 17:19:43 | MASTER-Tunka | (05h 08m 26.69s , -06d 47m 23.2s) | C | 60 | 16.2 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43187. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41271] GRB 251222A: Fermi GBM Final Real-time Localization
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43186 SUBJECT: GRB 251222A: Fermi GBM Final Real-time Localization DATE: 25/12/22 17:16:31 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 17:05:51 UT on 22 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251222A (trigger 788115956.26632 / 251222712). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 75.7, Dec = -5.3 (J2000 degrees, equivalent to J2000 05h 02m, -5d 17'), with a statistical uncertainty of 2.0 degrees. The angle from the Fermi LAT boresight is 81.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251222712/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251222712/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251222712/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43186. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41270] EP251220a: PRIME upper limit
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43185 SUBJECT: EP251220a: PRIME upper limit DATE: 25/12/22 16:55:31 GMT FROM: N. Passaleva at Sapienza University of Rome <niccolo.passaleva(a)uniroma1.it> N. Passaleva (U Rome), O. Guiffreda (UMD), M. El Kabir (U Rome), J. Durbak (UMD), E. Troja (U Rome), A. S. Kutyrev (NASA/GSFC), S. B. Cenko (NASA/GSFC) We observed the field of the optical counterpart (Sánchez Álvarez et al. GCN 43167) of the fast X-ray transient EP251220a (Liu et al., GCN 43162) in J filter with PRIME. Observations started ~35h after the trigger. Using Two Micron All Sky Survey (2MASS) nearby stars for preliminary calibration we do not detect any uncatalogued source down to J>20.5 AB (3-sigma) not corrected for galactic extinction at the position of the candidate reported by Sánchez Álvarez et al. (GCN 43167), Kumar et al. (GCN 43169), Busmann et al. (GCN 43181), van Hoof et al. (GCN 43182), An et al. (GCN 43184). PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa at the South African Astronomical Observatory (SAAO) (Kutyrev et al. 2023, Yama et al. 2023, Durbak et al. 2024). We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/43185. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41269] EP251220a: VLT/FORS2 spectroscopic redshift z = 2.375
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43184 SUBJECT: EP251220a: VLT/FORS2 spectroscopic redshift z = 2.375 DATE: 25/12/22 16:47:08 GMT FROM: Aishwarya L Thakur at INAF-IAPS, Rome <aishth(a)outlook.com> J. An (NAOC), A. Saccardi (CEA/Irfu), R. A. J. Eyles-Ferris (U. Leicester), D. B. Malesani (DAWN/NBI and Radboud), M. Ferro (INAF-OABr), A. P. C. van Hoof (Radboud), A. L. Thakur (INAF-IAPS), D. Xu (NAOC), report on behalf of the Stargate collaboration: We observed the optical counterpart of EP251220a (Sánchez Álvarez et al., GCN 43167; Rakotondrainibe et al., GCN 43170; Busmann et al., GCN 43181; van Hoof et al., GCN 43182) detected by the Einstein Probe (Liu et al., GCN 43162) using the ESO VLT UT1 (Antu) equipped with the FORS2 spectrograph. Our observation started at 01:02:04 UT on 2025 December 22 (40.6 hr after the EP trigger). A series of spectra was obtained with the 300V grism covering the range 3500-6500 AA and consisted of 4 exposures of 600 s each. In the acquisition image (40.46 hr after trigger), we measure for the transient a magnitude r = 21.80 +- 0.05 (AB), calibrated against nearby stars from the Pan-STARRS catalogue, and not corrected for Galactic extinction. This value indicates little decay compared to the other reported optical observations. In a preliminary reduction of the data, we identify multiple absorption features, including Lyα broad trough likely due to H I, as well as Si II, C II, and Al II, at a common redshift of 2.375, which we thus suggest to be the redshift for this transient. The COLIBRÍ redshift upper limit (Sánchez Álvarez et al., GCN 43167) is thus fully consistent with our spectroscopic measurement. We acknowledge expert support from the ESO observing staff in Paranal, particularly Juan Carlos Olivares and Maria Jose Rain. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495) View this GCN Circular online at https://gcn.nasa.gov/circulars/43184. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41268] GRB 251221A: PRIME near-infrared observation
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43183 SUBJECT: GRB 251221A: PRIME near-infrared observation DATE: 25/12/22 16:02:42 GMT FROM: N. Passaleva at Sapienza University of Rome <niccolo.passaleva(a)uniroma1.it> N. Passaleva (U Rome), O. Guiffreda (UMD), M. El Kabir (U Rome), J. Durbak (UMD), E. Troja (U Rome), A. S. Kutyrev (NASA/GSFC), S. B. Cenko (NASA/GSFC) Following the Fermi/Swift (Fermi GBM team, GCN 43164; Ambrosi et al., GCN 43166) detection, we observed the transient field in J and H filter with PRIME. Observations started ~15.5 hours after the initial trigger. Using Two Micron All Sky Survey (2MASS) nearby stars for preliminary calibration we detect an uncatalogued source at the position reported by Rakotondrainibe et al. (GCN 43168) and Volnova et al. (GCN 43180). We derived the following magnitudes not corrected for galactic extinction: J = 20.27 ± 0.09 H = 19.52 ± 0.04 PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa at the South African Astronomical Observatory (SAAO) (Kutyrev et al. 2023, Yama et al. 2023, Durbak et al. 2024). We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/43183. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41267] EP251220a: NOT optical observations
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43182 SUBJECT: EP251220a: NOT optical observations DATE: 25/12/22 14:18:06 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> A. P. C. van Hoof (Radboud), G. Corcoran (UCD), J. An (NAOC), R. A. J. Eyles-Ferris (U. Leicester), D. B. Malesani (DAWN/NBI and Radboud), D. Xu (NAOC), J. Sanchez-Sierras (Radboud), P. G. Jonker (Radboud), A. Martin-Carrillo (UCD), A. Kadela (NOT and NBI), report on behalf of a larger collaboration: We observed the optical counterpart (Álvarez et al., GCN 43167; Kumar et al., GCN 43169; Rakotondrainibe et al., GCN 43170; Busmann et al., GCN 43181) of EP251220a (Liu et al., GCNs 43162, 43172) with the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. A sequence of 4x300 s exposures were taken in SDSS r-band starting on 2025-12-21 at 19:37:19.906 UT (~35.18 hr since the EP trigger). The source is well detected in the stacked image with a preliminary photometry of r = 21.79 +/- 0.05 (AB), calibrated against nearby stars from the Pan-STARRS catalog and not corrected for Galactic extinction. Our photometry is consistent with the temporal index found by Rakotondrainibe et al. (GCN 43170). View this GCN Circular online at https://gcn.nasa.gov/circulars/43182. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41266] EP251220a: FTW optical and NIR observations
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43181 SUBJECT: EP251220a: FTW optical and NIR observations DATE: 25/12/22 13:41:22 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Xander J. Hall (CMU), Julius Gassert (LMU/CMU), Brendan O'Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report: We observed the counterpart of EP251220a (Liu et al. GCN 43162, Sánchez Álvarez et al. GCN 43167, Liu et al. GCN 43172) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J-band simultaneously for 5 x 180 s starting at 2025-12-21T18:45:36 UT (1.43 days after the trigger). We detect the counterpart in the r and i-band and measure an r-band magnitude of r = 21.94 +/- 0.12 AB mag. Our measurements are consistent with the reports by Lipunov et al. (GCN 43163), Sánchez Álvarez et al. (GCN 43167), Kumar et al. (GCN 43169), and Rakotondrainibe et al. (GCN 43170). The magnitude is calibrated against the PS1 catalog and not corrected for Galactic extinction. We thank Michael Schmidt from the Wendelstein Observatory for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/43181. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41265] GRB 251221A: UAFO and Mondy optical upper limit
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43180 SUBJECT: GRB 251221A: UAFO and Mondy optical upper limit DATE: 25/12/22 12:03:11 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. A. Volnova (IKI), A. Kochergin (UAFO IAA), E. Klunko (ISTP), A. S. Pozanenko (IKI), N. S. Pankov (HSE, IKI) report on behalf of IKI-GRB-FuN: We observed the field of GRB 251221A (Fermi GBM team, GCN 43164; Ambrosi et al., GCN 43166) with the RC-500 (0.5m) telescope of Ussuriysk Astrophysical Observatory (UAFO) and with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) taking several frames in R-band. The observations started on Dec. 21 at UT 15:18:04 with RC-500 and at UT 17:25:26, i.e., ~ 0.4-0.5 days after the Swift/BAT trigger. In the stacked images in the Swift/XRT error circle (Goad et al., GCN 43175) we do not detect the optical counterpart reported previously by Rakotondrainibe et al. (GCN 43168). Preliminary photometry and observational details are the following: Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope fwhm" (mid,days) (n*s) (3sigma) 2025-12-21 15:18:04 0.42900 60*60 R n/d n/d 19.7 UAFO/RC-500 2.7 2025-12-21 17:25:26 0.51314 18*120 R n/d n/d 22.1 Mondy/AZT-33IK 2.6 The photometry is based on several nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43180. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41264] GRB 251221A: Swift-XRT refined Analysis
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43179 SUBJECT: GRB 251221A: Swift-XRT refined Analysis DATE: 25/12/22 05:38:12 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), S. Campana (INAF-OAB), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 4.3 ks of XRT data for GRB 251221A, from 122 s to 56.3 ks after the trigger. The data comprise 8 s in Windowed Timing (WT) mode (taken while Swift was slewing), with the remainder in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=1.13 (+0.17, -0.14). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.49 (+0.19, -0.18). The best-fitting absorption column is 1.11 (+0.24, -0.22) x 10^22 cm^-2, in excess of the Galactic value of 7.3 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 6.8 x 10^-11 (9.5 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.11 (+0.24, -0.22) x 10^22 cm^-2 Galactic foreground: 7.3 x 10^21 cm^-2 Excess significance: 2.8 sigma Photon index: 1.49 (+0.19, -0.18) If the light curve continues to decay with a power-law decay index of 1.13, the count rate at T+24 hours will be 1.9 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.3 x 10^-13 (1.8 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/01426088. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/43179. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41263] EP251221a: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43178 SUBJECT: EP251221a: Einstein Probe detection of a fast X-ray transient DATE: 25/12/22 04:07:09 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C. Y. Dai (NJU), J. H. Wu (GU), W. F. Wen (SZTU), H. Q. Cheng, W. D. Zhang (NAO,CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP251221a. The transient triggered EP-WXT (ID: 01709250307) at 2025-12-21T21:39:06 (UTC). The WXT position of the source is R.A. = 104.531 deg, DEC = 23.374 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The analysis of the WXT data shows that the event lasted for ~100 s. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 8.1 x 10^20 cm^-2 and a photon index of 0.45 (-0.34/+0.36). The derived average unabsorbed 0.5-4 keV flux is 7.28 (-2.23/+3.30) x 10^(-10) erg/s/cm^2 (All errors are 1 sigma uncertainties.). Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/43178. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41262] GRB 251221A: Swift/UVOT Upper Limits
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43177 SUBJECT: GRB 251221A: Swift/UVOT Upper Limits DATE: 25/12/22 01:04:18 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M.H. Siegel (PSU) and Ambrosi (INAF-IASFPA) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 251221A 143 s after the BAT trigger (Ambrosi et al., GCN Circ. 43166). No optical afterglow consistent with the XRT position (Goad et al., GCN Circ 43175) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 143 292 147 >20.5 white 143 1541 366 >21.1 v 631 1584 65 >19.6 b 570 1521 45 >19.4 u 301 1497 169 >19.5 w1 680 1647 40 >19.1 m2 655 847 39 >19.5 w2 606 1572 78 >19.6 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 1.088 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/43177. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41261] Fermi Gamma-ray Burst Monitor trigger 788028118/251221696 is not a GRB
by GCN Circulars 21 Dec '25

21 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43176 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 788028118/251221696 is not a GRB DATE: 25/12/21 22:01:00 GMT FROM: Bagrat Mailyan at Florida Tech <mbagrat(a)gmail.com> B. Mailyan (Florida Tech) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 788028118/251221696 at 16:41:53.69 UT on 21 December 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to particle activity." View this GCN Circular online at https://gcn.nasa.gov/circulars/43176. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41260] GRB 251221A: Enhanced Swift-XRT position
by GCN Circulars 21 Dec '25

21 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43175 SUBJECT: GRB 251221A: Enhanced Swift-XRT position DATE: 25/12/21 20:38:47 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team. Using 1499 s of XRT Photon Counting mode data and 2 UVOT images for GRB 251221A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 101.42771, +0.73217 which is equivalent to: RA (J2000): 06h 45m 42.65s Dec (J2000): +00d 43' 55.8" with an uncertainty of 2.1 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at https://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/43175. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41259] GRB 251221A: Fermi GBM Observation
by GCN Circulars 21 Dec '25

21 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43174 SUBJECT: GRB 251221A: Fermi GBM Observation DATE: 25/12/21 20:13:03 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> A. Holzmann Airasca (UniTrento and INFN Bari) and S. Bala (USRA) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 05:24:28.61 UT on 21 December 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251221A (trigger 787987473/251221225). which was also detected by Swift (Ambrosi et al. 2025, GCN 43166). The Fermi GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 96 degrees. The GBM light curve consists of a single peak with a duration (T90) of about 28 s (50-300 keV). The time-averaged spectrum from T0-13.3 to T0+23.6 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.1 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 330 +/- 100 keV. The event fluence (10-1000 keV) in this time interval is (4.2 +/- 0.5)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.4 s in the 10-1000 keV band is 2.0 +/- 0.2 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 240 +/- 130 keV, alpha = -1.0 +/- 0.2 and beta = -1.8 +/- 0.2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/43174. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41258] GRB 251221B: Fermi GBM Final Real-time Localization
by GCN Circulars 21 Dec '25

21 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43173 SUBJECT: GRB 251221B: Fermi GBM Final Real-time Localization DATE: 25/12/21 18:56:51 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 18:46:21 UT on 21 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251221B (trigger 788035586.997792 / 251221782). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 274.7, Dec = -21.4 (J2000 degrees, equivalent to J2000 18h 18m, -21d 23'), with a statistical uncertainty of 7.2 degrees. The angle from the Fermi LAT boresight is 86.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251221782/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251221782/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251221782/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43173. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41257] EP251220a: EP-FXT follow-up observation
by GCN Circulars 21 Dec '25

21 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43172 SUBJECT: EP251220a: EP-FXT follow-up observation DATE: 25/12/21 15:05:25 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. C. Liu (THU), Y. Wang (PMO), H.Y. Liu, H. W. Pan (NAO,CAS) on behalf of the Einstein Probe team: EP-FXT performed a follow-up observation of EP251220a (detected by EP-WXT, GCN 43162; and followed by MASTER-Net observations, COLIBRI telescope and GOTO; GCN 43163, GCN 43167, GCN 41369, GCN 43170) about 19 hours after the WXT detection, with an exposure time of 2.6 ks. The FXT telemetry data show that an uncatalogued source was detected within the WXT error circle at R.A. = 17.3189, DEC = 19.0923 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT X-ray spectrum of this uncatalogued source can be fitted with an absorbed powerlaw with a hydrogen column density fixed at the Galactic value of 4.8x 10^20 cm^-2 and a photon index of 1.7 (+0.5/-0.5). The derived unabsorbed 0.5-10 keV flux is approximately 3.6 (+2.4/-1.2) x 10^-13 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/43172. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41256] GRB 251220B: SVOM/GRM observation of a short burst
by GCN Circulars 21 Dec '25

21 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43171 SUBJECT: GRB 251220B: SVOM/GRM observation of a short burst DATE: 25/12/21 13:31:39 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Marius Brunet, Sebastien Guillot (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a short burst GRB 251220B (SVOM trigger reference: sb25122004) at 2025-12-20T23:38:04.700 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN#43160). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 0.28 +0.15/-0.10 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251220B.png In addition, the position of this burst, as determined by Fermi/GBM(RA= 251.4, DEC= 47.9, ERR=6.4), is located at about 135 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/43171. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41255] EP251220a: COLIBRÍ confirmation of fading and photometric redshift upper limit of z < 3.4
by GCN Circulars 21 Dec '25

21 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43170 SUBJECT: EP251220a: COLIBRÍ confirmation of fading and photometric redshift upper limit of z < 3.4 DATE: 25/12/21 11:43:02 GMT FROM: Ny Avo Rakotondrainibe at LAM <nyavo.rakotobe(a)gmail.com> Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Enrique Moreno Méndez (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Nikos Mandarakas (LAM), Margarita Pereyra (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM). We reobserved the field of EP251220a (Liu et al., GCN Circ. 43162) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-12-21 04:35 to 07:13 UTC (from 20.13 to 22:51 hours after the trigger) and obtained 8, 32, 8, 32, and 5 minutes of exposure, respectively, in the g, r, i, z, and y filters. The data were reduced and coadded with the ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. Compared to our first epoch of observations (Sánchez Álvarez et al., GCN Circ. 43167), the afterglow has faded with a temporal index of -1.38 +/- 0.25. This confirms the association with the X-ray transient. We detect the afterglow in all filters. After correcting for the Galactic foreground extinction corresponding to a reddening of E(B-V) = 0.037 mag (Schlafly & Finkbeiner 2011) and fitting a power-law with a SMC dust extinction model to the grizy-bands, we estimate a photometric redshift upper limit of z < 3.4. We therefore encourage follow-up observations. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/43170. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41254] EP 251220a: GOTO optical counterpart detection
by GCN Circulars 21 Dec '25

21 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43169 SUBJECT: EP 251220a: GOTO optical counterpart detection DATE: 25/12/21 11:08:01 GMT FROM: Amit Kumar at The Open University, UK <amitkundu515(a)gmail.com> A. Kumar, G. Ramsay, M. Kennedy, D. O'Neill, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) that serendipitously covered the field of EP 251220a (Liu et al. GCN 43162). The observations were conducted with GOTO-North at 2025-12-20 19:51:42 UT (11.4 hours post-trigger), consisting of 4x45s exposures in the GOTO L-band (400-700 nm). Difference imaging was performed using deeper template observations of the same pointings. We detect the optical counterpart of EP 251220a (Álvarez et al., GCN 43167) in the GOTO L-band at 3σ, with a magnitude of 20.7 ± 0.3 (AB). Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/43169. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41253] GRB 251221A: COLIBRÍ detection of the optical counterpart
by GCN Circulars 21 Dec '25

21 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43168 SUBJECT: GRB 251221A: COLIBRÍ detection of the optical counterpart DATE: 25/12/21 06:43:18 GMT FROM: Ny Avo Rakotondrainibe at LAM <nyavo.rakotobe(a)gmail.com> Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Enrique Moreno Méndez (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Nikos Mandarakas (LAM), Margarita Pereyra (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM): We imaged the field of the Fermi/Swift GRB 251221A (Fermi GBM team, GCN Circ. 43164; Ambrosi et al., GCN Circ. 43166) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-12-21 05:25:46 to 06:08 UTC (from 75 seconds to 43 minutes after the trigger) and obtained 1690 seconds of simultaneous exposure in the r and z filters. The data were reduced and coadded with the ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detected an uncatalogued, fading source at RA (J2000) = 06:45:42.73 = 101.42804 deg Dec (J2000) = +00:43:54.8 = 0.73189 deg with an uncertainty of 0.5 arcsec and preliminary magnitudes of: r > 24.2 (3-sigma) z = 22.26 +/- 0.18 The XRT uncertainty region (Ambrosi et al., GCN Circ. 43166) has a 90% confidence radius of 1.8 arcsec, and this source is 2.3 arcsec from the center. We suggest therefore that this is the optical counterpart of the GRB. The lack of detection in r is consistent with the high Galactic extinction in this direction of A_V = 3.1 mag (Schlafly et al. 2011). We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/43168. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41252] EP 251220a: COLIBRÍ detection of the optical counterpart
by GCN Circulars 21 Dec '25

21 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43167 SUBJECT: EP 251220a: COLIBRÍ detection of the optical counterpart DATE: 25/12/21 05:53:22 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Fredd Sánchez Álvarez (UNAM), Ny Avo Rakotondrainibe (LAM), Leonardo García García (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Jean-Grégoire Ducoin (CPPM), Enrique Moreno Méndez (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Nikos Mandarakas (LAM), Margarita Pereyra (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM). We imaged the field of the fast X-ray transient EP251220a (Liu et al., GCN Circ. 43162) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-12-21 04:08 UTC to 04:35 UTC (from 19.70 to 20.13 hr after the trigger) and obtained 18 minutes of simultaneous exposure in the r and z filters. The data were reduced, coadded and analyzed with the COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and was not corrected for Galactic extinction. In the stacked image, we detect an uncataloged source at the FXT uncertainty region (Liu et al., GCN Circ. 43162) at RA (J2000) = 01:09:16.60 = 17.31915 deg Dec (J2000) = +19:05:32.3 = 19.09231 deg with an uncertainty of about 0.5 arcsec and with preliminary magnitudes of r = 21.15 +/- 0.02 z = 20.72 +/- 0.04 We suggest that this is the counterpart of the fast X-ray transient. Further observations will be necessary to detect fading. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/43167. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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