December 2025 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 41354] GRB 251230A: Enhanced Swift-XRT position
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43263 SUBJECT: GRB 251230A: Enhanced Swift-XRT position DATE: 25/12/30 08:02:58 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team. Using 1379 s of XRT Photon Counting mode data and 1 UVOT images for GRB 251230A, 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 = 179.89737, +11.43831 which is equivalent to: RA (J2000): 11h 59m 35.37s Dec (J2000): +11d 26' 17.9" with an uncertainty of 2.2 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/43263. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41353] GRB 251230A: Early optical counterpart detection by LCO.
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43262 SUBJECT: GRB 251230A: Early optical counterpart detection by LCO. DATE: 25/12/30 05:52:21 GMT FROM: ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994(a)gmail.com> Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Rahul Gupta (NASA GSFC), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES) on behalf of a larger collaboration. We observed the field of the GRB 251230A triggered by Swift (Lanava et al., GCN 43252) in B, V, and r filter of the 1-m Sinistro telescope and 0.4-m SCICAM QHY600 at the Las Cumbres Observatory Global Telescope (LCOGT) node located at South African Astronomical Observatory (SAAO). The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel) and the 0.4 m SCICAM QHY600 is equipped with 9576 x 6388 pixel CCD (FOV: 1.9 x 1.2 degrees, scale: 0.74 arcsec/pixel). Observations began on October 13, 2025, starting from 0.84 hours after the GRB trigger. Further observations are still ongoing. We clearly detect the optical transient (OT) reported by GCNs (Lanava et al., GCN 43252, Li et al., GCN 43255, Masi et al., GCN 43260). ----------------------------------------------------------------------------------------------------- |Date| |JDstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ----------------------------------------------------------------------------------------------------- 2025-12-30 2461039.59159 0.84 1 x 300 r r = 17.20 +/- 0.01 2025-12-30 2461039.60333 1.12 2 x 300 r r = 17.64 +/- 0.11 ----------------------------------------------------------------------------------------------------- The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43262. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41352] EP-WXT trigger 01709250662 Mephisto and 50cm telescope follow-up
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43261 SUBJECT: EP-WXT trigger 01709250662 Mephisto and 50cm telescope follow-up DATE: 25/12/30 04:51:48 GMT FROM: elagioia(a)ynu.edu.cn Yuan Fang, Edoardo P. Lagioia, Jialei Zheng, Xian Liu, Jinghua Zhang, Chunsheng Xiao, Brajesh Kumar, Guowang Du, Xingzhu Zou, Xinlei Chen, Xufeng Zhu, Tao Wang, Yehao Cheng, Xinzhong Er, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team The EP-WXT trigger 01709250662 (trigger time 2025-12-27T16:37:01), identified as a stellar flare associated to the High Proper Motion star PM J11474+6644 (Wang. C. et al., GCN 43241; Y.-H. I. Yin et al., GCN 43247) has been observed with the following facilities of the Yunnan University, located at the Lijiang Observatory: the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) and one of the twin 50cm RC telescopes. A set of simultaneous multi-band (vrz and ugi) frames have been collected with Mephisto from 2025-12-27 UTC18:18:51 (~ 1.75 hr after the trigger) and continued until 2025-12-27 UTC 18:22:58. Preliminary analysis of the scientific frames indicate the following observed magnitudes: ----------------------------------------------- Start_Time(UT) | Band | Exp(s) | Mag (AB) --------------------|-------|--------|--------- 2025-12-27T18:18:51 | v | 45 | 16.88 2025-12-27T18:18:54 | r | 45 | 13.78 2025-12-27T18:18:53 | z | 45 | 11.10 2025-12-27T18:22:55 | u | 45 | 17.66 2025-12-27T18:22:58 | g | 45 | 14.65 2025-12-27T18:22:57 | i | 45 | 11.60 ----------------------------------------------- Ten frames in g-band have also been collected with the 50cm telescope starting from 2025-12-27 UTC 16:46:08 (~ 9 minutes after the trigger) and continued till 2025-12-27 UTC 16:54:40, for total duration of ~ 8.5 minutes. The first epoch observation shows a g-band luminosity of 14.02 mag, while the last epoch indicates 14.24 mag. Time series observations allowed to build a light curve in g-band which shows an average decay rate of ~ 0.024 mag/min. It is worth noticing that the g-band (AB) magnitude of PM J11474+6644 listed in the SIMBAD database is equal to 15.505 Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6m 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/43261. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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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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