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

[vsnet-grb-info 38331] GRB 250430A : MITSuME Akeno optical upper limits
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40302 SUBJECT: GRB 250430A : MITSuME Akeno optical upper limits DATE: 25/05/01 11:06:05 GMT FROM: hagio.h.ffca(a)m.isct.ac.jp H. Hagio, I. Takahashi, M. Sasada, H. Seki, S. Joshima, Y. Kubo, A. Ochi, R. Kato, Y. Yatsu and N. Kawai (Science Tokyo) report on behalf of the MITSuME collaboration: We observed the field of GRB 240430A detected by Swift/BAT (Parsotan et al. GCN 40292) with the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno. The observation started at 2025-04-30 17:31:53 UT (32 seconds after the Swift/BAT trigger). We stacked the images with good conditions. We did not detect any obvious point sources at the position reported by Parsotan et al., GCN 40292, Odeh et al., GCN 40295, Wang et al., GCN 40299, and Garnichey et al., GCN 40301. We obtained the 5-sigma limits of the stacked images as follows: T0+[min] | MID-UT | T-EXP[sec] | 5-sigma limits ------------------------------------------------------------------------------------------------ 15.1 | 2025-04-30 17:46:27 | 620 | g'>18.2, Rc>18.2, Ic>17.8 78.5 | 2025-04-30 18:29:51 | 2880 | g'>19.3, Rc>19.6, Ic>19.0 ------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the trigger T-EXP: Total Exposure time We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ; https://github.com/MNiwano/Eclaire). View this GCN Circular online at https://gcn.nasa.gov/circulars/40302. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38330] GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40301 SUBJECT: GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767 DATE: 25/05/01 10:00:04 GMT FROM: Andrea Saccardi at CEA/Irfu <andrea.saccardi(a)cea.fr> M. Garnichey (LUX-Paris Obs.), A. Saccardi (CEA/Irfu), B. Schneider (LAM), G. Corcoran (UCD), N. Habeeb (Leicester), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), N. R. Tanvir (Leicester), A. L. Thakur (INAF/IAPS), A. de Ugarte Postigo (LAM) report on behalf of the Stargate collaboration: We observed the optical counterpart (Parsotan et al., GCN 40292; Odeh et al., GCN 40295) of GRB 250430A / EP250430a (Parsotan et al., GCN 40292; Wang et al., GCN 40299) with the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000 - 21000 AA, and consist of 4 exposures of 600 s each. The observation mid time was 2025 May 01 at 04:00:11 UT (10.87 hr after the Swift/BAT trigger). In a 3x30-s image, taken in the r band at a mid time of 10.34 hr after the trigger, the optical counterpart is detected at RA, Dec 233.3872, -18.1184 which is equivalent to: RA (J2000) = 15:33:32.93 Dec (J2000) = -18:07:06.3 These coordinates are in good agreement with those reported by Odeh et al. (GCN 40295). We measure a preliminary AB magnitude r = 21.97 +/- 0.06, calibrated against nearby stars from the Pan-STARRS catalog. In a preliminary reduction of the spectra, we observe a continuum over the entire covered wavelength range, fainter in the UVB and VIS arms than in the NIR. A few absorption features are detected, which we interpret as the Mg II doublet (2796, 2804) and Fe II (2374, 2383, 2587, 2600), all at the common redshift z = 0.767. No emission lines are observed across the whole covered spectrum. We note the presence of a catalogued object in the Legacy Survey DR10 at a position consistent with the optical afterglow. The magnitudes of the galaxy are g = 24.59 +/- 0.25, r = 23.22 +/- 0.10, i = 21.96 +/- 0.05, and z = 21.35 +/- 0.04, and its centroid is 0.5" away from the optical afterglow position. Our spectroscopic redshift measurement is consistent with the photometric redshift value provided of 0.89 +/- 0.11. This object is the likely host galaxy of GRB 250430A, though we notice that its red colors and lack of emission lines are not typical of a long (collapsar) GRB host. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Celia Desgrange, Rodrigo Palominos, and Camila de Sa Freitas. 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/40301. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38329] SVOM/sb25043004: EP-FXT observations
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40300 SUBJECT: SVOM/sb25043004: EP-FXT observations DATE: 25/05/01 08:55:01 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S.Q. Jiang, H.Y. Liu, R.D. Liang, H.W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation on SVOM/sb25043004 at 2025-04-30T17:26:25 (UTC), about 7 hours after the SVOM/ECLAIRs trigger (Liang et al. GCN # 40287). Two previously known X-ray sources and an uncatalogued X-ray source are detected within the ECLAIRs error circle. Preliminary analysis on these source are automatically conducted, and details are listed as follows. Source 1: EPF_J180814.9-384246 (1eRASS J180815.0-384254) RA (J2000): 272.0610 Dec (J2000): -38.7126 Flux: 1.77 x 10^-13 erg/cm^2/s (observed, 0.5-10 keV) Flux_error: 3.7 x 10^-14 erg/cm^2/s (1 sigma) Note: The source is spatially consistent with 1eRASS J180815.0-384254, which has a flux of 8.34 (+4.22/-3.17, 1 sigma) x 10^-14 erg/cm^2/s (0.2-2.3 keV). Source 2: EPF_J180840.1-384205 (1eRASS J180840.7-384211) RA (J2000): 272.1683 Dec (J2000): -38.7025 Flux: 4.88 x 10^-13 erg/cm^2/s (observed, 0.5-10 keV) Flux_error: 5.9 x 10^-14 erg/cm^2/s (1 sigma) Note: The source is spatially consistent with 1eRASS J180840.7-384211, which has a flux of 1.41 (+0.52/-0.41, 1sigma) x 10^-13 erg/cm^2/s (0.2-2.3 keV). Source 3: EPF_J180801.1-384501 (uncataloged) RA (J2000): 272.0057 Dec (J2000): -38.7511 Flux: 2.44 x 10^-13 erg/cm^2/s (observed, 0.5-10 keV) Flux_error: 4.6 x 10^-14 erg/cm^2/s (1 sigma) Note: The upper limit given by eROSITA DR1 is 1.71 x 10^-13 erg/cm^2/s (0.2-2.3 keV). The position uncertainties of the above sources are about 10 arcsec in radius (90% C.L. statistical and systematic). 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/40300. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38328] EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40299 SUBJECT: EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission DATE: 25/05/01 08:11:44 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C. Y. Wang (THU), H. L. Peng (NJNU), Y. Q. Zhao (USTC, PRIC), W. Yuan (NAO, CAS), 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 EP250430a. The WXT detection was not triggered onboard due to the closeness of the source position to the bright X-ray source Sco X-1, but was made in the onground analysis of the telemetry data later. No automated follow-up X-ray observation was performed. The WXT position of the source is R.A. = 233.399 deg, DEC = -18.130 deg (J2000) with an uncertainty of 2.9 arcmin in radius (90% C.L. statistical and systematic), which is offset by 1.0 arcmin from the Swift/XRT position of the likely long GRB 250430A (Lipunov et al., GCN 40291; Parsotan et al., GCN 40292; Kawabata et al., GCN 40294; Odeh et al., GCN 40295). The X-ray rise time precedes the GRB trigger time by approximately 23 seconds, and the X-ray duration is longer than that of the GRB by about 30 seconds. The X-ray emission peaked at 2025-04-30T17:31:05.5 (UTC). The consistency of EP250430a and GRB 250430A in position and time suggests EP250430a to be the X-ray counterpart of GRB 250430A. Note that the source parameters given above are only approximate and detailed analysis is onging. The averaged WXT spectrum in 0.5-4 keV can be fitted by an absorbed power law model with a photon index of 2.37 (+0.61, -0.54) and a column density of 3.80 (+1.50, -1.31) x 10^21 cm^-2. The average unabsorbed 0.5-4 keV flux is about 1.63 (+0.69, -0.36) x 10^-10 erg/cm^2/s. These parameters derived are at the 1-sigma confidence level. Further observations with the Follow-up X-ray Telescope (FXT) on board EP may be considered at a later stage. Contact transient advocate (TA) for EP250430a is C. Y. Wang (wang-cy22(a)mails.tsinghua.edu.cn) and please contact the TA for information regarding the EP observation of this source. 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/40299. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38327] GRB 250424A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40298 SUBJECT: GRB 250424A: CALET Gamma-Ray Burst Monitor detection DATE: 25/05/01 03:19:12 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> GRB 250424A: CALET Gamma-Ray Burst Monitor detection S. Nakahira (JAXA), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The long GRB 250424A (Swift detection: Cenko et al., GCN Circ. 40224; Swift-BAT refined analysis: Markwardt et al., GCN Circ. 40255; AstroSat CZTI detection: Harsha et al., GCN Circ. 40231; Konus-Wind detection: Ridnaia et al., GCN Circ. 40243; EIRSAT-1 GMOD Detection: McKenna et al., GCN Circ. 40249; SVOM/GRM observation: Jin-Peng et al., GCN Circ. 40252) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 06:52:04.323 UTC on 24 April 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1429512582/index.html). The burst signal was seen by all CGBM detectors. The burst light curve shows a single pulse that starts at T+2.5 sec, peaks at T+8.4 sec, and ends at T+27.5 sec. The T90 and T50 durations measured by the SGM data are 13.5 +/- 0.8 sec and 4.6 +/- 0.2 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1429512582/ The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/40298. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38326] IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40297 SUBJECT: IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/04/30 22:01:21 GMT FROM: Alicia Mand at IceCube/UW-Madison <aemand(a)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-250429A (https://gcn.nasa.gov/circulars/40280) in a time range of 1000 seconds centered on the alert event time (2025-04-29 15:14:55.620 UTC to 2025-04-29 15:31:35.620 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-250429A.The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250429A is 1.4e-01 GeV cm^-2 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 (2025-04-28 15:23:15.620 UTC to 2025-04-30 15:23:15.620 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250429A is 1.7e-01 GeV cm^-2 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/40297. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38325] IceCube-250426A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40296 SUBJECT: IceCube-250426A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/04/30 21:59:47 GMT FROM: Alicia Mand at IceCube/UW-Madison <aemand(a)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-250426A (https://gcn.nasa.gov/circulars/40253) in a time range of 1000 seconds centered on the alert event time (2025-04-26 17:36:38.160 UTC to 2025-04-26 17:53:18.160 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-250426A. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250426A is 1.4e-01 GeV cm^-2 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 9e+04 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2025-04-25 17:44:58.160 UTC to 2025-04-27 17:44:58.160 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250426A is 1.7e-01 GeV cm^-2 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/40296. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38324] GRB 250430A: AKO Optical Afterglow Detection
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40295 SUBJECT: GRB 250430A: AKO Optical Afterglow Detection DATE: 25/04/30 19:20:09 GMT FROM: Mohammad Odeh at Al Khatim Observatory M44 <mshodeh(a)gmail.com> Mohammad Odeh (Al-Khatim Observatory, AKO, operated by the International Astronomical Center in Abu Dhabi, UAE), and Nidhal Guessoum (American University of Sharjah, UAE), report: We observed the field of GRB 250430A detected by Swift/BAT (Parsotan et al., GCN 40292), using our 0.36m f/7.7 robotic telescope. The observation session began on 30 April 2025 at 17:52 UT, 21 minutes after the trigger. We obtained multiple 180-second exposures using the Ic filter. An uncatalogued object is faintly visible at the location below, which could be the optical afterglow: R.A. (J2000): 15:33:32.95 Dec. (J2000): -18:07:05.9 The following observation was calculated using the Atlas catalogue as a reference: ---------------------------------------------------------------------------- - ObsTime (mid), Exposure (sec), Filter, Mag ---------------------------------------------------------------------------- - 2025-04-30T18:29:42Z, 15 x 180s (stacked), Ic, 18.6 +/- 0.22 ---------------------------------------------------------------------------- - The magnitude is not corrected for galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40295. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38323] GRB 250430A: Kanata optical upper limit
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40294 SUBJECT: GRB 250430A: Kanata optical upper limit DATE: 25/04/30 18:52:29 GMT FROM: Koji Kawabata at HASC,Hiroshima U <kawabtkj(a)hiroshima-u.ac.jp> K. S. Kawabata, T. Hori, T. Nakaoka (Hiroshima Univ.) report on behalf of Kanata team: We performed optical imaging polarimetry to the field of the GRB 180720B (Parsotan et al. GCN 40292; Lipunov et al. GCN 40291) from 2025-04-30 17:34:03 UT (162 seconds after the trigger) with HONIR attached to the 1.5-m Kanata telescope at Higashi-Hiroshima Observatory, Japan. We did not detect any new optical source up to a limiting magnitude of Rc = 16.0 (3-sigma; Vega mag) at the position of the UVOT source in our first 30 second exposure. View this GCN Circular online at https://gcn.nasa.gov/circulars/40294. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38322] EP 250427A: Optical counterpart detection by LCO.
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40293 SUBJECT: EP 250427A: Optical counterpart detection by LCO. DATE: 25/04/30 18:45:08 GMT FROM: ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994(a)gmail.com> Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES), Rahul Gupta (NASA GSFC) on behalf of a larger collaboration. We observed the field of the EP 250427A triggered by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission and Fermi (Wang et al. GCN 40257, Ravasio et al. GCN 40262) in the r filter of the 0.4 m SCICAM QHY600 at the Las Cumbres Observatory Global Telescope (LCOGT) node located at South African Astronomical Observatory (SAAO). 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) but we only used the FOV of 30 x 30 arcmin for our observation. Observations began on April 27, 2025, starting 19.90 hours after the GRB trigger. We clearly detect the optical transient (OT) reported by GCNs (Perez-Garcia et al., GCN #40259), TRT (Liu et al., GCN #40260), COLIBRÍ (Becerra et al., GCN #40261), REM (Brivio et al., GCN #40264), LCO (Pérez-Fournon et al., GCN #40267), LT (Qiang Xi et al., GCN #40269), GIT (Swain et al., GCN #40270), COLIBRÍ (Magnani et al., GCN #40271), Lesedi (S. de Wet et al., GCN #40272), FTW (Busmann et al., GCN #40273), OHP/T193 (Amram et al., GCN #40275, Amram et al., GCN #40288, Eappachen et al., GCN #40289) in our r band image. ------------------------------------------------------------------------------------------------------ |Date| |JD start| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ------------------------------------------------------------------------------------------------------ 2025-04-27 2460793.48177 19.91 2 x 600 r r = 19.05 +/- 0.07 ------------------------------------------------------------------------------------------------------ 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/40293. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38321] GRB 250430A: Swift detection of a burst with optical counterpart
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40292 SUBJECT: GRB 250430A: Swift detection of a burst with optical counterpart DATE: 25/04/30 18:07:07 GMT FROM: Tyler Parsotan at NASA GSFC <tyler.parsotan(a)nasa.gov> T. M. Parsotan (GSFC), C. Gronwall (PSU), R. Gupta (NASA GSFC), N. J. Klingler (GSFC/UMBC/CRESSTII), M. J. Moss (GSFC), K. L. Page (U Leicester), M. H. Siegel (PSU) and M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 17:31:21 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250430A (trigger=1308754). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 233.428, -18.083 which is RA(J2000) = 15h 33m 43s Dec(J2000) = -18d 04' 59" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi peak structure with a duration of about 20 sec. The peak count rate was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 17:33:37.5 UT, 157.3 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 233.38611, -18.11784 which is equivalent to: RA(J2000) = 15h 33m 32.67s Dec(J2000) = -18d 07' 04.2" with an uncertainty of 3.6 arcseconds (radius, 90% containment). This location is 190 arcseconds from the BAT onboard position, outside 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 (9.57 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.5 (+2.62/-2.27) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 161 seconds after the BAT trigger. There is a candidate afterglow in the list of sources generated on-board at RA(J2000) = 15:33:32.85 = 233.38688 DEC(J2000) = -18:07:06.2 = -18.11840 with a 90%-confidence error radius of about 1.10 arc sec. This position is 3.65 arc sec. from the center of the XRT error circle. The estimated magnitude is 19.44 with a 1-sigma error of about 0.35. No correction has been made for the expected extinction corresponding to E(B-V) of 0.092. Burst Advocate for this burst is T. M. Parsotan (tyler.parsotan AT nasa.gov). 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/40292. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38320] Swift GRB250430.73: Global MASTER-Net observations report
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40291 SUBJECT: Swift GRB250430.73: Global MASTER-Net observations report DATE: 25/04/30 18:03:45 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 (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB250430.73 (trigger No 1308754,15h 33m 42.72s , -18d 04m 58.8s, R=0.05) errorbox 1266 sec after notice time and 1293 sec after trigger time at 2025-04-30 17:52:33 UT, with upper limit up to 18.2 mag. The observations began at zenith distance = 77 deg. The sun altitude is -23.9 deg. The galactic latitude b = 29 deg., longitude l = 349 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2858290 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 1384 | MASTER-SAAO | C | 180 | 17.5 | 1583 | MASTER-SAAO | C | 180 | 18.2 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40291. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38319] EP250428b: FTW optical and NIR observations
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40290 SUBJECT: EP250428b: FTW optical and NIR observations DATE: 25/04/30 17:02:17 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU), and Antonella Palmese (Carnegie Mellon U.) report: We observed the localization of EP250428b (Liu et al., GCN 40277) 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 2025-04-30T01:13:27 UT (1.86 days after the trigger). We performed difference imaging in the r and i band with templates from the DESI Legacy Surveys and do not detect any new sources in the improved EP/FXT localization (Wu et al., GCN 40285). The 3 sigma upper limits are r > 23.9 mag i > 23.5 mag. These upper limits are consistent with previous reports (Lipunov et al., GCN 40278; Konno et al., GCN 40281; Moskvitin et al., GCN 40282; Xin et al., GCN 40283; Salgundi et al., GCN 40284). The magnitudes are calibrated against the PS1 catalog and not corrected for Galactic extinction. We thank Christoph Ries from the Wendelstein Observatory staff for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40290. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38318] EP250427a/GRB250427A: HCT optical follow-up
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40289 SUBJECT: EP250427a/GRB250427A: HCT optical follow-up DATE: 25/04/30 12:55:53 GMT FROM: anirudhsalgundi(a)gmail.com D. Eappachen (IIA), V. Swain (IITB), A. Salgundi (IITB), D.K. Sahu (IIA), A.P. Saikia (IITB), G. C. Anupama (IIA), V. Bhalerao (IITB), A. Balasubramanian (IIA), S. Barway (IIA), S. Bandari (IAO): We observed the field of EP250427a (Wang et al., GCN #40257), also detected by Fermi-GBM (Ravasio et al., GCN #40262) with the 2.0m Himalayan Chandra Telescope (HCT) of the Indian Astronomical Observatory (IAO). We obtained multiple exposures in the SDSS r' filter starting at 2025-04-29 22:10:49.88 UT (~2.77 days post trigger). We detected the source in our stacked image and obtained the following photometric result: | JD (mid) | Filter | Exposure (s) | Mag (AB) | Limiting Magnitude (AB) | | ----------------- | ------- | ------------------ | -------------- |--------------| | 2460795.433742 | r' | 5 x 240 | 21.70 +/- 0.12 | 21.9 | The magnitudes are calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our result is consistent with BOOTES-7 (Perez-Garcia et al., GCN #40259), TRT (Liu et al., GCN #40260), COLIBRÍ (Becerra et al., GCN #40261), REM (Brivio et al., GCN #40264), LCO (Pérez-Fournon et al., GCN #40267), LT (Qiang Xi et al., GCN #40269), GIT (Swain et al., GCN #40270), COLIBRÍ (Magnani et al., GCN #40271), Lesedi (S. de Wet et al., GCN #40272), FTW (Busmann et al., GCN #40273), OHP/T193 (Amram et al., GCN #40275). These observations were carried out under the ToO program HCT-2025-C1-P08. We thank the HCT staff for their support during the observations. The Indian Astronomical Observatory is operated by the Indian Institute of Astrophysics, Bengaluru, India. View this GCN Circular online at https://gcn.nasa.gov/circulars/40289. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38317] EP250427a / GRB 250427A: OHP/T193 continued photometric observations
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40288 SUBJECT: EP250427a / GRB 250427A: OHP/T193 continued photometric observations DATE: 25/04/30 12:54:46 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> P. Amram (LAM/AMU), S. Basa (Pytheas/OHP/LAM), C. Adami (LAM/Pytheas/AMU), N.A. Rakotondrainibe (LAM), S. Vergani (CNRS, Obs. de Paris, LUX), A. Saccardi (CEA/Irfu), J. T. Palmerio (CEA), B. Schneider (LAM), J. T. Palmerio (CEA/Irfu) report on behalf of the MISTRAL-GRB collaboration: We re-observed EP250427a / GRB 250427A (Wang et al. GCN 40257, Ravasio et al. GCN 40262) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager in blue setting. We obtained 3x900sec in the r’ band starting at 02:42:04UT on 2025-04-30 (T0+47.1 h after the trigger). The optical afterglow reported by Pérez-García et al. GCN 40259; Liu et al. GCN 40260; Becerra et al. GCN 40261; Brivio et al. GCN 40264; Chornock et al. GCN 40265; Saccardi et al. GCN 40266; Pérez-Fournon et al. GCN 40267; Xi et al. GCN 40269; Swain et al. GCN 40270; Magnani et al. GCN 40271; de Wet et al. GCN 40272; Busmann et al. GCN 40273, Wang et al. GCN40274, Amram et al. GCN 40275, Siegel et al. GCN 40279 is still detected at r = 21.50 +/- 0.18 mag (AB). The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitude is not corrected for Galactic extinction. We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular J. Schmitt, J.C. Brunel, F. Huppert, F. Moreau, Stephane Favard, Jean Pierre Troncin, Jean Balcaen and Yoann Degot-Longhi. View this GCN Circular online at https://gcn.nasa.gov/circulars/40288. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38316] SVOM/sb25043004: SVOM detection of a X-ray transient
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40287 SUBJECT: SVOM/sb25043004: SVOM detection of a X-ray transient DATE: 25/04/30 11:39:06 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Y. Liang (PMO), W. Zheng (Berkeley), O. Godet, S. Guillot (IRAP), C. Plasse, J. T. Palmerio (CEA) on behalf of the SVOM mission team. SVOM/ECLAIRs triggered and located the X-ray transient sb25043004 (SVOM burst-id sb25043004) starting at 2025-04-30T10:40:57.1 UTC (Tb). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The source was only detected by the Image Trigger (IMT), which produced a sequence of 3 alerts. IMT provided the alert with the best signal-to-noise-ratio (SNR) of 8.96 in the [5-8] keV energy band over a time window of 327.68 seconds starting at Tb. The localization of the best alert is R.A., Dec. 272.104, -38.6635 degrees: R.A. (J2000) = 18h08m25.13s Dec. (J2000) = -38d39m48.60s with a 90% confidence level (C.L.) radius of 8.82 arcmin (including systematic error of 2 arcmin added in quadrature). SVOM slewed to the source. MXT began observing the field after the slew. The analysis of the recorded images will be published in a future circular gathering information on the follow-up of the SVOM optical instruments. VT began observing the field after the slew. The analysis of the recorded images will be published in a future circular gathering information on the follow-up of the SVOM optical instruments. 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. The Burst Advocate (BA) on shift for this burst is Weikang Zheng: weikang(a)berkeley.edu. Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/40287. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38315] Fermi trigger No 767623859: Global MASTER-Net observations report
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40286 SUBJECT: Fermi trigger No 767623859: Global MASTER-Net observations report DATE: 25/04/30 09:31:00 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB250429.54 (trigger No 767623859,22h 03m 43.92s , -05d 28m 01.2s, R=31.13) errorbox 73850 sec after notice time and 73884 sec after trigger time at 2025-04-30 09:22:19 UT, with upper limit up to 19.5 mag. The observations began at zenith distance = 42 deg. The sun altitude is -22.3 deg. The galactic latitude b = -45 deg., longitude l = 55 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2856527 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 73905 | 2025-04-30 09:22:19 | MASTER-OAFA | (21h 58m 38.65s , -10d 46m 32.6s) | C | 40 | 17.6 | 73915 | 2025-04-30 09:22:19 | MASTER-OAFA | (22h 07m 54.27s , -10d 23m 06.7s) | C | 60 | 19.2 | 73983 | 2025-04-30 09:23:37 | MASTER-OAFA | (22h 01m 48.50s , -14d 36m 44.5s) | C | 40 | 17.8 | 73993 | 2025-04-30 09:23:37 | MASTER-OAFA | (22h 11m 12.61s , -14d 13m 10.4s) | C | 60 | 19.5 | 74058 | 2025-04-30 09:24:53 | MASTER-OAFA | (22h 13m 36.90s , -16d 29m 55.1s) | C | 40 | 18.0 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40286. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38314] EP250428b: refined analysis of the EP-FXT follow-up observation
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40285 SUBJECT: EP250428b: refined analysis of the EP-FXT follow-up observation DATE: 25/04/30 09:16:55 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. Y. Wu, M. J. Liu, T. Zhao, Y. J. Song (NAO, CAS), H. Z. Wu (HUST), C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: After the EP-WXT detection of the fast X-ray transient EP250428b (Liu et al., GCN 40277), a follow-up observation was performed by EP-FXT at 2025-04-29T14:04:00 (UTC), about 32 hours after the detection, with an exposure time of 3.0 ks. On-ground analysis of the EP-FXT data identified an uncatalogued X-ray source within the EP-WXT error circle, at the coordinates (J2000): R.A., Dec. = 220.4575, 2.0989 deg, with an uncertainty of 10 arcsec (radius, 90% confidence level, including both statistical and systematic errors). The unabsorbed 0.5-10 keV flux is estimated to be 1.2 (+0.4, -0.4) x 10^-13 erg/cm^2/s, derived using an absorbed power law model with the hydrogen column density fixed to the Galactic value of 3.77 x 10^20 cm^-2 and the photon index fixed at 2.0, due to the limited photon statistics. All uncertainties quoted above are at the 90% confidence level. 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/40285. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38313] EP250428b: GROWTH-India telescope optical upper limit
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40284 SUBJECT: EP250428b: GROWTH-India telescope optical upper limit DATE: 25/04/30 07:54:42 GMT FROM: anirudhsalgundi(a)gmail.com A. Salgundi (IITB), V. Swain (IITB), D. Eappachen (IIA), A.P. Saikia (IITB), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of the EP250428b (Liu et al., GCN #40277) with the 0.7m GROWTH-India Telescope (GIT). Observation started at 2025-04-29T18:21:59 UT, about 1.51 days after the trigger. We obtained single image of 360s in r' filter. The following upper limit was obtained: |MJD (mid)| Filter| Exposure (s)| Limiting Magnitude (AB)| | ----------------- | ----------- |------- | ------------------ | 60794.7652662038| r'| 360| 20.5 The magnitude is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. The upper limit is consistent with MASTER (Lipunov et al., GCN #40278), LAST (Konno et al., GCN #40281), SAO RAS (Moskvitin et., GCN #40282), SVOM/VT (Xin et al., GCN #40283). The GROWTH India Telescope (GIT, Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/40284. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38312] EP250428b: SVOM/VT upper limit
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40283 SUBJECT: EP250428b: SVOM/VT upper limit DATE: 25/04/30 01:39:45 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao(NAOC), M. J. Liu, Q. Y. Wu, T. Zhao, Y. J. Song (NAO, CAS), H. Z. Wu (HUST), C. C. Jin (NAO, CAS), X. H. Han,Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC) report on behalf of the SVOM team and the Einstein Probe (EP) team: SVOM/VT conducted ToO follow-up observations of the EP250428b(Liu et al., GCN 40277). The observation started on 2025-04-29T17:26:22 UT, 2025 Apr 29, in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously. With the effective exposure time of 2500 seconds, no any new sources were detected in EP/FXT error box (Liu et al., GCN 40277) in stacked images with the 3 sigma upper limit of VT_B=23.2 mag and VT_R=23.0 mag, compared to Legacy survey, at the mid time of 1.487 days after the transient time. This result is consistent with the reports (Konno et al., GCN 40281, Moskvitin et al., GCN 40282). 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. 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/40283. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38311] EP250428b: SAO RAS optical upper limit
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40282 SUBJECT: EP250428b: SAO RAS optical upper limit DATE: 25/04/29 23:39:13 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. S. Moskvitin, O. I. Spiridonova (SAO RAS) report on behalf of the GRB follow-up team. We observed the field of the X-ray transient EP250428b (Liu et al., GCN 40277) with the SAO RAS 1-m telescope Zeiss-1000 on April 29, 20:47:38--21:28:24 UT (t_mid - T0 = 1.6267 days). We obtained 7 x 300 sec. images in Rc band. Within the FXT error circle we detect several sources which are presented in the PanSTARRS images: R.A. Decl. R_mag +/- err #1 14:41:50.4 +02:06:18.0 20.20 +/- 0.10 #2 14:41:50.7 +02:06:13.4 22.86 +/- 0.21 #3 14:41:49.8 +02:05:55.9 22.57 +/- 0.17 Within the FXT error circle we did not detect any new sources down to the limiting magnitude of R_lim = 23.2 (calibrated against R2 magnitudes of nearby UNSO-B1 stars and not corrected for the MW extinction). View this GCN Circular online at https://gcn.nasa.gov/circulars/40282. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38310] EP250428b: LAST optical upper limit
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40281 SUBJECT: EP250428b: LAST optical upper limit DATE: 25/04/29 21:33:20 GMT FROM: Ruslan Konno at Weizmann Institute of Science <ruslankonno(a)gmail.com> R. Konno (WIS), S. Garrappa (WIS), E. A. Zimmerman (WIS), A. Horowicz (WIS), E. O. Ofek (WIS), S. Ben-Ami (WIS), D. Polishook (WIS), O. Yaron (WIS), S. Fainer (WIS), A. Krassilchtchikov (WIS), Y. M. Shani (WIS), E. Segre (WIS), A. Gal-Yam (WIS), S. Spitzer (WIS), and K. Rybicki (WIS) on behalf of the LAST Collaboration We report observations of the X-ray transient EP250428b (Liu et al., GCN 40277) with the Large Array Survey Telescope (LAST, Ofek et al. 2023; Ben-Ami et al. 2023). We observe the field of EP250428b using four telescopes, each with a FoV of 7.4 deg^2 and no filter (clear - similar to the GAIA Bp band). We began observations at 2025-04-29 18:25:34.194 UTC (T-T0 = 36.3h). We coadd a total of 160x20s exposure images and perform image subtraction using a reference image of the field. We do not detect any new optical source up to a limiting magnitude of 21.66 (AB) within the reported error regions of FXT and WXT. LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/). View this GCN Circular online at https://gcn.nasa.gov/circulars/40281. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38309] IceCube-250429A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40280 SUBJECT: IceCube-250429A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/04/29 19:07:06 GMT FROM: Giacomo Sommani at Ruhr-Universität Bochum <gsommani(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 25-04-29 at 15:23:15.63 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_GOLD alert stream. The average astrophysical neutrino purity for Gold alerts is 50%. This alert has an estimated false alarm rate of 0.496 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/140870_26727884.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 25-04-29 Time: 15:23:15.63 UT RA: 59.68 (+0.47/-0.57 deg 90% PSF containment) J2000 Dec: 25.32 (+0.39/-0.44 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/40280. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38308] GRB 250427A: Swift/UVOT Detection
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40279 SUBJECT: GRB 250427A: Swift/UVOT Detection DATE: 25/04/29 18:59:07 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M. H. Siegel (PSU) reports on behalf of the Swift UVOT team: Swift/UVOT observed the field of GRB 250427A detected by Einstein Probe (Wang et al., GCN Circ. 40257) starting 22.9 ks after the burst. A fading optical source was detected in the U-band consistent with the position of the uncatalogued X-ray source detected by Swift/XRT (D'Elia et al., GCN Circ 40268) and the optical afterglow detected by various facilities (Perez-Garcia et al., GCN Circ 40259; Liu et al., GCN Circ. 40260, Becerra et al,. GCN Circ. 40261; Brivio et al., GCN Circ 40264; Pérez-Fournon et al., GCN Circ. 40267; Xi et al., GCN Circ. 40269; Swain et al., GCN Circ 40270; de Wet et al., GCN Circ 40272; Busmann et al., GCN Circ. 40273; Amram et al., GCN Circ 40275). The preliminary detection and 3-sigma upper limits calculated using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag u 22960 28938 1622 18.74+/-0.07 u 136546 153119 1721 >20.47 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.209 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40279. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38307] EP250428b: Global MASTER-Net observations report
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40278 SUBJECT: EP250428b: Global MASTER-Net observations report DATE: 25/04/29 18:09:39 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 (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the EP250428b ( EP Team et al., GCN 40277) errorbox 285 sec after notice time and 1 days 41608 sec after trigger time at 2025-04-29 17:38:59 UT, with upper limit up to 17.6 mag. Observations started at twilight. The observations began at zenith distance = 64 deg. The sun altitude is -15.2 deg. The galactic latitude b = 53 deg., longitude l = 355 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2856874 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 128038 | 2025-04-29 17:38:59 | MASTER-Kislovodsk | (14h 39m 56.30s , +02d 18m 36.2s) | C | 60 | 17.1 | 128993 | 2025-04-29 17:54:54 | MASTER-Kislovodsk | (14h 39m 58.93s , +02d 19m 39.5s) | C | 60 | 17.5 | 129172 | 2025-04-29 17:57:52 | MASTER-Kislovodsk | (14h 39m 52.83s , +02d 19m 59.5s) | C | 60 | 17.6 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40278. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38306] EP250428b: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40277 SUBJECT: EP250428b: Einstein Probe detection of a fast X-ray transient DATE: 25/04/29 17:30:36 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> M. J. Liu, Q. Y. Wu, T. Zhao, Y. J. Song (NAO, CAS), H. Z. Wu (HUST), C. C. Jin (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 EP250428b (GCN Notice ID 01799135422). The WXT position of the source is R.A. = 220.479 deg, DEC = 2.09 deg (J2000) with an uncertainty of 2.7 arcmin in radius (90% C.L. statistical and systematic). A preliminary analysis of the EP-WXT data shows that the transient began at around 2025-04-28T06:05:31(UTC) and lasted for a few hundreds of seconds, with a peak flux of around 3 x 10^-10 erg/cm^2/s. The averaged WXT spectrum can be fitted by an absorbed power law model with a Galactic hydrogen column density of 3.77 x 10^20 cm^-2 and a photon index of 1.9 (+0.2, -0.2). The averaged unabsorbed 0.5-4 keV flux is 3.3 (+2.2, -1.3) x 10^-11 erg/cm^2/s. The uncertainties are at the 90% confidence level for the above parameters. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed from 2025-04-29T13:41:27 (UTC). Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 220.4586 deg, DEC = 2.1002 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 is received. The contact TA of EP250428b is Q. Y. Wu. Please contact him via email qywu(a)bao.ac.cn if needed. 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/40277. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38305] Fermi-LAT Gamma-ray Observations of IceCube-250426A
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40276 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-250426A DATE: 25/04/29 11:02:04 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg), S. Garrappa (Weizmann Institute of Science) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC250426A neutrino event (GCN 40254) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 2025-04-26 17:44:58.16 UTC (T0) with J2000 position RA = 296.37 (+0.53, -0.50) deg, Decl. = 20.7 (+0.52, -0.52) deg 90% PSF containment. No cataloged gamma-ray sources are found within the 90% IC250426A localization error (The Fourth Fermi-LAT catalog, 4FGL-DR4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5 sigma) new excess emission (> 100 MeV) within the IC250426A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC250426A best-fit position, the >100 MeV flux upper limit (95% confidence) is <6.95e-10 ph cm^-2 s^-1 for ~16-years (2008-08-04 / T0), <4.67e-08(<3.56e-07) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this region will continue. For this analysis, the Fermi-LAT contact person is L. Pfeiffer (leonard.pfeiffer at uni-wuerzburg.de). The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/40276. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38304] EP250427a / GRB 250427A: OHP/T193 photometric observations
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40275 SUBJECT: EP250427a / GRB 250427A: OHP/T193 photometric observations DATE: 25/04/29 08:49:00 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> P. Amram (LAM/AMU), C. Adami (LAM/Pytheas/AMU), S. Vergani (CNRS, Obs. de Paris, LUX), S. Basa (Pytheas/OHP/LAM), A. Saccardi (CEA/Irfu), B. Schneider (LAM) report on behalf of the MISTRAL-GRB collaboration: We observed EP250427a / GRB 250427A (Wang et al. GCN 40257, Ravasio et al. GCN 40262) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager in blue setting. We obtained 2x60sec + 120sec + 3x600sec in the r’ band starting at 02:55:47UT on 2025-04-28 (T0+23.3 h after the trigger). The optical afterglow reported by Perez-Garcia et al. GCN 40259; Liu et al. GCN 40260; Becerra et al. GCN 40261; Brivio et al. GCN 40264; Chornock et al. GCN 40265; Saccardi et al. GCN 40266; Pérez-Fournon et al. GCN 40267; Xi et al. GCN 40269; Swain et al. GCN 40270; Magnani et al. GCN 40271; de Wet et al. GCN 40272; Busmann et al. GCN 40273 is detected at a preliminar value of r = 20.3 +/- 0.15 mag (AB). The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitude is not corrected for Galactic extinction. We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Jean Balcaen and Yoann Degot-Longhi. View this GCN Circular online at https://gcn.nasa.gov/circulars/40275. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38303] EP250427a: EP-FXT follow-up observations
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40274 SUBJECT: EP250427a: EP-FXT follow-up observations DATE: 25/04/29 07:11:52 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. Wang (PMO, CAS), D. Y. Li (NAO, CAS), Y. Q. Zhao (USTC, PRIC), J. H. Wu (GZHU), Y. Liu (NAO, CAS) behalf of the Einstein Probe (EP) team: After the EP-WXT detection of the fast X-ray transient EP250427a (Wang et al., GCN 40257), two follow-up observations have been conducted by EP-FXT. The first follow-up observation was performed at 2025-04-27T08:38:17 (UTC), about 5.6 hours after the trigger, with an exposure time of 4.1 ks. On-ground analysis of the EP-FXT data identified an uncatalogued X-ray source within the EP-WXT error circle, at the coordinates (J2000): R.A., Dec. = 277.2728, 7.5625 deg, with an uncertainty of about 10 arcsec (radius, 90% confidence level, including both statistical and systematic errors). The 0.5-10 keV spectrum can be fitted with an absorbed power-law model, with the column density nH fixed at the Galactic value of 3.01e21 cm^-2, and a photon index of 1.89(+0.18, -0.18). The unabsorbed 0.5-10 keV flux is 4.2 (+0.6, -0.5) e-12 erg/s/cm^2. This is consistent with the Swift-XRT refined analysis (D'Elia et al. GCN 40268). The FXT localization is consistant with the positions of the optical conterparts. The detection of the optical and IR counterpart has been reported in several GCNs (Lipunov et al. GCN 40258; Perez-Garcia et al. GCN 40259; Liu et al. GCN 40260; Becerra et al. GCN 40261; Brivio et al. GCN 40264; Saccardi et al. GCN 40266; Pérez-Fournon et al. GCN 40267; Xi et al. GCN 40269; Swain et al. GCN 40270; Magnani et al. GCN 40271; de Wet et al. GCN 40272), and the event was also detected as the sub-threshold GRB 250427A by Fermi/GBM (Ravasio et al. GCN 40262). And the redshift of EP240527a was measured to be 1.519 (Chornock et al. GCN 40265) or 1.520 (Saccardi et al. GCN40266). The second follow-up observation was performed at 2025-04-28T14:13:49 (UTC), about 35.1 hours after the trigger, with an exposure time of 5.9 ks. The 0.5-10 keV spectrum can also be fitted with an absorbed power-law model, with nH fixed at the Galactic value of 3.01e21cm^-2, and a photon index fixed of 1.66 (+0.44, -0.41). The unabsorbed 0.5-10 keV flux is 5.0 (+2.1, -1.3) e-13 erg/s/cm^2. All uncertainties quoted above are at the 90% confidence level. 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/40274. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38302] EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40273 SUBJECT: EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart DATE: 25/04/28 17:06:44 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU) and Antonella Palmese (Carnegie Mellon U.) report: We observed the counterpart of EP250427a (Wang et al., GCN 40257; Lipunov et al., GCN 40258; Perez-Garcia et al., GCN 40259; Liu et al., GCN 40260; Becerra et al., GCN 40261; Brivio et al., GCN 40264; Saccardi et al., GCN 40266; Pérez-Fournon et al., GCN 40267; Xi et al., GCN 40269; Swain et al., GCN 40270; Magnani et al., GCN 40271; de Wet et al., GCB 40272) which was also seen as sub-threshold GRB 250427A by Fermi/GBM (Ravasio et al., GCN 40262) 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 2025-04-28T01:48:29 UT (0.92 days after the trigger). We detect the counterpart at r = (20.17 +/- 0.03) mag i = (19.75 +/- 0.03) mag J = (18.91 +/- 0.03) mag. The r and i band magnitudes are calibrated against the PS1 catalog and the J band is calibrated with the 2MASS Catalog. All magnitudes are provided in the AB system and are not corrected for Galactic extinction. We thank Michael Schmidt from the Wendelstein Observatory staff for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40273. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38301] EP250427a: Lesedi optical counterpart detection
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40272 SUBJECT: EP250427a: Lesedi optical counterpart detection DATE: 25/04/28 13:43:45 GMT FROM: Simon de Wet at University of Cape Town <simdewet(a)gmail.com> S. de Wet (DTU space), N. Erasmus (SAAO), W.X. Li (NAOC), N.C. Sun (UCAS,NAOC) report: The SAAO 1-m Lesedi telescope located at Sutherland, South Africa, obtained 2x60 s exposures with the Mookodi low-resolution spectrograph and imager in each of the g,r and i bands of EP250427a (Wang et al., GCN 40257) beginning at 00:22:13 UTC on 2025 April 28 (0.87 days post-trigger). We detect the optical counterpart reported by Perez-Garcia et al. (GCN 40259), Liu et al. (GCN 40260), Becerra et al. (GCN 40261), Ghosh et al. (GCN 40263), Brivio et al. (GCN 40264), Chornock et al. (GCN 40265), Saccardi et al. (GCN 40266), Perez-Fournon et al. (GCN 40267), and Xi et al. (GCN 40269) with the following AB magnitudes: g = 20.66 +/- 0.09 r = 20.07 +/- 0.07 i = 19.69 +/- 0.08 Data was taken with the SAAO's 1-m Lesedi robotic telescope with the Mookodi low-resolution spectrograph and imager [1] as part of the SAAO “IO” rapid follow-up program [2]. We thank the SAAO IO team members including N. Erasmus, S. Potter, C. van Gend, H. Worters, S. Chandra, D. Cunnama, M. Hlakola, P. Rabe, R. Julie for making these observations possible. [1] https://doi.org/10.1117/1.JATIS.10.2.025005 [2] https://doi.org/10.1117/12.3015250 View this GCN Circular online at https://gcn.nasa.gov/circulars/40272. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38300] EP250427A: COLIBRÍ Continuing Optical Observations
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40271 SUBJECT: EP250427A: COLIBRÍ Continuing Optical Observations DATE: 25/04/28 12:30:11 GMT FROM: Francesco Magnani at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work(a)gmail.com> Francesco Magnani (CPPM), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM)report: We continued our observational campaign of EP250427a (Wang et al., GCN Circ. 40257) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico on the night of 2025-04-28 UTC. We observed from 2025-04-28 09:16 to 2025-04-28 09:26 UTC (29.6 to 29.8 hours after the trigger) and obtained 3 stacks in filter r, i, and g, of 3 minutes each. Our observations were performed under regular weather conditions. The data were co-added with the COLIBRÍ pipeline and analysed in STDWeb/STDPipe (karpov 2025), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction. In the optical position (Perez-Garcia et al., GCN Circ. 40259; Liu et al., GCN Circ. 40260; Becerra et al., GCN Circ. 40261; Brivio et al., GCN Circ. 40264; Chornock et al., GCN Circ. 40265; Saccardi et al., GCN Circ. 40266; Pérez-Fournon et al., GCN Circ. 40267; and Xi et al., GCN Circ. 40269), we measured: r = 20.55 +/- 0.05 Compared to our first epoch (Becerra et al., GCN Circ. 40261), we estimate the fading nature of the OT with a temporal index ~1.2, consistent with the value reported by Swain et al. (GCN Circ. 40270). Further observations and analysis are ongoing. We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40271. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38299] GRB250427A/EP250427a GIT optical afterglow detection:
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40270 SUBJECT: GRB250427A/EP250427a GIT optical afterglow detection: DATE: 25/04/28 12:10:05 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> V. Swain (IITB), A. Salgundi (IITB), Y. Wagh (IITB), A.P. Saikia (IITB), D. Eappachen (IIA), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of of EP 250427a (Wang et al., GCN #40257), also detected by Fermi-GBM (Ravasio et al., GCN #40262) with 0.7m GROWTH-India Telescope (GIT) in g and r filters. We started the observation at 2025-04-27 19:19:43 UT, i.e., 15.68 hrs after the EP trigger. The source is detected at EP position and the position reported by TRT network (Liu et al., GRB #40260) and the photometry result follows as: | JD (mid) | t-t0 (hours) | Filter | Exposure (s) | Mag (AB) | | ----------------- | ----------- |------- | ------------------ | -------------- | | 2460793.305359 | 15.68 | r' | 360 | 19.66+/- 0.10 | | 2460793.318148 | 15.98 | g' | 360 | 20.47+/- 0.10 | | 2460793.366678 | 17.15 | r' | 360 | 20.00+/- 0.09 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. The object is decaying with powerlaw index of 1.15 +/- 0.04. Further observations are under way. Our result is consistent with BOOTES-7 (Perez-Garcia et al., GCN #40259), TRT (Liu et al., GCN #40260), COLIBRÍ (Becerra et al., GCN #40261), REM (Brivio et al., GCN #40264), LCO (Pérez-Fournon et al., GCN #40267) LT (Qiang Xi et al., GCn #40269). The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/40270. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38298] EP250427a: LT optical counterpart detection
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40269 SUBJECT: EP250427a: LT optical counterpart detection DATE: 25/04/28 07:34:08 GMT FROM: qiang xi <xiqiang051(a)gmail.com> Qiang Xi (UCAS), I. Pérez-Fournon, F. Poidevin, D.S. Aguado, A. López-Oramas, D. Nespral (IAC and ULL), N.C. Sun, Z.X. Niu (UCAS and NAOC), W.X. Li, Y.N. Wang (NAOC): We observed the field of the Einstein Probe WXT event EP250427a (Wang et al., GCN circ. 40257), using the 2.0-meter Liverpool Telescope (LT) located at the Observatorio del Roque de los Muchachos, La Palma, Spain. Observations were carried out with the IO:O instrument, starting on 2025-04-28 at 03:34UT. We obtained a series of 3x60s exposures in each of the u, g, r, i, and z filters. An uncatalogued source is clearly detected in griz bands at the optical counterpart position first reported by Perez-Garcia et al. (GCN circ. 40259) and with other optical and near-infrared detections reported by Liu et al. (GCN circ. 40260), Becerra et al. (GCN circ. 40261), Brivio et al. (GCN circ. 40264), Chornock et al. (GCN circ. 40265), Saccardi et al. (GCN circ. 40266), Pérez-Fournon et al. ( GCN circ. 40267). The preliminary r-band photometry for this source is reported below, calibrated with the Pan-STARRS catalog, and not corrected for Galactic extinction. | UTC start | mag | error | filter | exposure time (sec) | | ----------------------- | ----- | ----- | ------ | ------------------- | | 2025-04-28 03:42:36.919 | 20.14 | 0.17 | SDSS-r | 3×60 | View this GCN Circular online at https://gcn.nasa.gov/circulars/40269. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38297] GRB 250427A: Swift-XRT refined Analysis
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40268 SUBJECT: GRB 250427A: Swift-XRT refined Analysis DATE: 25/04/27 17:49:43 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> V. D'Elia (ASI-SSDC), E. Ambrosi (INAF/IASFPA), K.L. Page (U Leicester), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), M. A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), A. D'Ai (INAF-IASFPA) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: We have analysed 1.7 ks of XRT data for the Einstein Probe/WXT-detected burst GRB 250427A, from 22.9 ks to 28.9 ks after the Einstein Probe/WXT trigger. The data are entirely in Photon Counting (PC) mode. We found an uncatalogued X-ray source within the estimated 3-sigma EP-WXT error region. We find an XRT position: RA, Dec = 277.27280, +7.5632 which is equivalent to: RA (J2000): 18h 29m 05.47s Dec (J2000): +07° 33′ 47.6″ with an uncertainty of 3.9 arcsec (radius, 90% confidence). This position is 6.9 arcsec from the EP-WXT position, and consistent with the X-ray counterpart found in EP/FXT data (Wang et al. GCN 40257) and with the optical counterpart reported by Perez-Garcia et al. (GCN 40259), Becerra et al. (GCN 40261), Ghosh et al. (GCN 40263), Brivio et al. (GCN 40264). The light curve is consistent with a constant source with a hint of fading in the last segment. However, given the corresponding optical counterpart and the measured redshift, we believe this to be the X-ray afterglow. Further observations are planned. A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.78 (+0.39, -0.28). The best-fitting absorption column is consistent with the Galactic value of 2.9 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 4.3 x 10^-11 (5.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.9 (+/-1.3) x 10^21 cm^-2 Galactic foreground: 2.9 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.78 (+0.39, -0.28) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00019750. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40268. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38296] EP250427a / GRB 250427A: LCO optical counterpart detection
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40267 SUBJECT: EP250427a / GRB 250427A: LCO optical counterpart detection DATE: 25/04/27 16:30:09 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), and A. López-Oramas (IAC and ULL) Following the detection of the fast X-ray transient EP250427a (Wang et al., GCN circ. 40257), detected also by Fermi-GBM, GRB 250427A (Ravasio et al., GCN circ. 40262), we observed the field with one of the two Las Cumbres Observatory Global Telescope network (LCOGT) 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at McDonald Observatory (Texas) in the SDSS r filter. The observation started at 2025-04-27 10:10:47 UTC, about 6.53 hours after the EP-WXT trigger. An uncatalogued source is clearly detected at the optical counterpart position first reported by Perez-Garcia et al. (GCN circ. 40259) and with other optical and near-infrared detections reported by Liu et al. (GCN circ. 40260), Becerra et al. (GCN circ. 40261), Brivio et al. (GCN circ. 40264), Chornock et al. (redshift of z = 1.519, GCN circ. 40265), and Saccardi et al. (redshift of z = 1.520, GCN circ. 40266). We measure the following magnitude, calibrated against Pan-STARRS DR2 stars, that is not corrected for Galactic extinction: Date | UT start | mag | error | filter | exposure time (sec) | ------------------------------------------------------------------------ 2025-04-27 10:10:47 18.55 0.10 r 180 This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF). View this GCN Circular online at https://gcn.nasa.gov/circulars/40267. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38295] EP250427a / GRB 250427A: VLT/X-shooter redshift confirmation z = 1.520
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40266 SUBJECT: EP250427a / GRB 250427A: VLT/X-shooter redshift confirmation z = 1.520 DATE: 25/04/27 15:39:47 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> A. Saccardi (CEA/Irfu), V. Abril-Melgarejo (LUX-Paris Obs.), Z. P. Zhu (NAOC), V. D’Elia (ASI/SSDC), A. J. Levan (Radboud and Warwick), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), B. Schneider (LAM), N. R. Tanvir (Leicester), A. L. Thakur (INAF/IAPS), S. D. Vergani (LUX-Paris Obs.), K. Wiersema (Hertfordshire), D. Xu (NAOC), report on behalf of the Stargate collaboration: We observed the optical counterpart (Perez-Garcia et al., GCN 40259; Liu et al., GCN 40260; Becerra et al., GCN 40261; Brivio et al., GCN 40264) of EP250427a / GRB 250427A (Wang et al., GCN 40257; Ravasio et al., GCN 40262) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21,000 AA, and consist of 2 exposures of 600 s each. The observation mid time was 2025 Apr 27.394 UT (5.80 hr after the GRB). In a 30-s image taken in the r band at a mid time of 5.61 hr after the trigger, we measure a magnitude r = 18.40 +- 0.02 AB, calibrated against nearby stars from the Pan-STARRS catalog. In a preliminary reduction of the spectra, we clearly observe a bright continuum over the entire covered wavelength range, detected at high S/N. The sightline is rich with intervening absorption systems, in particular C IV absorbers (1548,1550 doublet) are detected at z = 1.146, 1.222, 1.231, 1.405, 1.407, 1.518, and 1.520. The highest-redshift system is only securely detected in C IV and Si IV (at both z = 1.518 and 1.520). There is a possible indication of Lyman alpha absorption at the very blue end of the spectrum, with very low column density (much less than a DLA). The system at z = 1.405/1.407 is on the other hand the strongest and has detection in many species at both high and low ionization, including Si II, C II, Si IV, C IV, Fe II, Al II, Al III, Mg II and Mg I, as well as a rich velocity structure. No emission lines are visible at any of the above mentioned redshifts. Our data are therefore in good agreement with the results and the redshift value z = 1.520 already reported by Chornock et al. (GCN 40265) using the Keck telescope. We acknowledge expert and efficient support from the observing staff at Paranal, in particular Boris Haeussler, Francesca Lucertini, Rodrigo Romero, and Elisa Garro. View this GCN Circular online at https://gcn.nasa.gov/circulars/40266. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38294] EP250427A/GRB250427A: Keck/LRIS redshift
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40265 SUBJECT: EP250427A/GRB250427A: Keck/LRIS redshift DATE: 25/04/27 14:11:22 GMT FROM: Ryan Chornock at UC Berkeley <chornock(a)berkeley.edu> R.Chornock, E. Hammerstein, X. Guo (UC Berkeley) report: We observed the optical afterglow (GCNs 40258, 40259, 40260, 40261, 40263, 40264) of EP250427a (GCN 40257)/GRB 250427a (GCN 40262) using the Low-Resolution Imaging Spectrometer on the Keck-I telescope at a mean time of 12:36UT on 2025 Apr 27. Observations covered the range 3140-10300 Angstroms. A continuum is well detected across the full spectral range with many absorption lines present. We identify a strong doublet at observed wavelengths of 3900.3,3906.7 Angs as CIV at z=1.519 from the highest redshift system detected. There are also many lines (C II, C IV, Fe II, Mg I, Mg II) from a stronger low-redshift system at z=1.406. Further analysis is ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/40265. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38293] EP250427a: REM optical/NIR afterglow detection
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40264 SUBJECT: EP250427a: REM optical/NIR afterglow detection DATE: 25/04/27 13:23:16 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio, M. Ferro, P. D’Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of EP250427a detected by EP/WXT (Wang et al., GCN 40257), also seen by Fermi/GBM (Ravasio et al., GCN 40262) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 April 27 at 07:20:13 UT (i.e. 3.7 h after the burst). From preliminary photometry, we detect the optical/NIR counterpart (Perez-Garcia et al., GCN 40259; Liu et al., GCN 40260; Becerra et al., GCN 40261) with the following magnitudes: r = 18.1 +/- 0.3 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 3.7 h after the trigger, H = 15.3 +/- 0.2 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 3.7 h after the trigger, View this GCN Circular online at https://gcn.nasa.gov/circulars/40264. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38292] GRB 250424A: LCO optical observation
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40263 SUBJECT: GRB 250424A: LCO optical observation DATE: 25/04/27 13:05:34 GMT FROM: ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994(a)gmail.com> Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES), Rahul Gupta (NASA GSFC) on behalf of a larger collaboration. We observed the field of the GRB 250424A triggered by Swift (Cenko et al., GCN 40224), AstroSat CZTI (Harsha et al., GCN 40231), Konus-Wind (Ridnaia et al., GCN 40243) and EIRSAT-1 GMOD (McKenna et al., GCN 40249)in B, V, r filters of the 1-meter Sinistro at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Cerro Tololo Interamerican Observatory, Chille. The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel). Observations began on , starting from 2025-04-24, 17.8 hours after the GRB trigger. Observation for later epochs are still going on. We clearly detect the optical transient (OT) reported by GCNs (Francile et al., GCN 40222; Cenko et al., GCN 40224; Brivio et al., GCN 40225; Becerra et al., GCN 40226; Saccardi et al., GCN 40228; de Wet et al., GCN 40229; Ducoin et al., GCN 40230; and D. Turpin et al., GCN 40240, Dutton et al., GCN Circ. 40241, Siegel et al., GCN 40244) in our B, V, r band images. ------------------------------------------------------------------------------------------------------ |Date| Start JD |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ------------------------------------------------------------------------------------------------------ 2025-04-25 2460790.52730 17.78 1 x 900 V V = 21.31+/- 0.08 2025-04-25 2460790.78105 23.87 1 x 900 B B = 22.07+/- 0.08 2025-04-25 2460790.79155 24.12 1 x 900 r r = 21.04 +/- 0.05 ------------------------------------------------------------------------------------------------------ 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/40263. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38291] GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40262 SUBJECT: GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection DATE: 25/04/27 12:34:44 GMT FROM: mariaedvige.ravasio(a)ru.nl M. E. Ravasio (Radboud Univ.), E. Burns (LSU), Adam Goldstein (USRA) and P.G. Jonker (Radboud Univ.) report on behalf of the Fermi-GBM Team: Fermi-GBM had full spatial and temporal coverage of the transient EP250427a detected by EP-WXT (Wang et al., GCN 40257). There was no Fermi-GBM onboard trigger around the EP starting time at T0=2025-04-27T03:38:45 UTC. The GBM Targeted Search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [-50;+500] s from the EP T0. A transient was found most significantly at T0+53 s on a 32 s timescale, with a false alarm rate of 5.9e-05 Hz (although there is evidence for signal at ~T0-10s). The localisation is consistent with the EP one, with a spatial association probability of 98.5%. Among the three spectral templates tested, the transient was best-fit with a "soft" spectrum (i.e., a Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) for a GRB. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/40262. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38290] EP250427A: COLIBRÍ Optical Detection
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40261 SUBJECT: EP250427A: COLIBRÍ Optical Detection DATE: 25/04/27 10:34:16 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Benjamin Schneider (LAM), Jean-Luc Atteia (IRAP), Margarita Pereyra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA/IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of EP250427A (Wang et al., GCN Circ. 40257) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico on the night of 2025-04-27 UTC. We observed from 2025-04-27 08:54 to 09:27 UTC (T+5.3 to T+5.8 hours after the trigger) and obtained 3-minute exposures in the g, r, and i filters (for each one). Our observations were performed under regular weather conditions. The data were coadded with the COLIBRÍ pipeline and analysed in STDWeb/STDPipe (Karpov 2025), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction. Within the EP/FXT (Wang et al., GCN Circ. 40257) error region, we detect an uncatalogued source at R.A. = 277.2746 deg, DEC = 7.5639 deg (J2000), with an uncertainty of 0.4 arcsec, with magnitudes of: g= 18.91 +/- 0.04 r= 18.42 +/- 0.04 i= 17.88 +/- 0.04 This source is consistent with the candidate reported by BOOTES-7 (Perez-Garcia et al., GCN Circ. 40259) and TRT (Liu et al., GCN Circ. 40260). Further observations and analysis are ongoing. We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40261. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38289] EP250427a: TRT optical counterpart detection
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40260 SUBJECT: EP250427a: TRT optical counterpart detection DATE: 25/04/27 10:13:08 GMT FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn> X. Liu, Z.P. Zhu, S.Q. Jiang (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), S.Y. Fu (HUST), J. An, Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang, D. Xu (NAOC) report on behalf of a large collaboration: We observed the field of EP250427a (Wang et al., GCN 40257), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. Observations started at 07:24:25.019 UTC on 2025-04-27, i.e., ~3.67 hr after the EP/WXT trigger and 6x200 s frames in the Sloan r-band were obtained. An uncatalogued and varying optical source is detected within the EP/FXT error circle (Wang et al., GCN 40257) at coordinates R.A. (J2000) = 18:29:05.73 Dec. (J2000) = +7:33:46.27 with an uncertainty of ~ 0.5 arcsec. Preliminary photometry shows that the source has r ~ 17.9 mag at 3.96 hr post-trigger, calibrated with Pan-STARRS DR2 catalog and not corrected for Galactic extinction. We think that this source is the optical counterpart of the event. View this GCN Circular online at https://gcn.nasa.gov/circulars/40260. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38288] EP 250427a: BOOTES-7 optical afterglow candidate
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40259 SUBJECT: EP 250427a: BOOTES-7 optical afterglow candidate DATE: 25/04/27 10:11:14 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> I. Perez-Garcia, A. J. Castro-Tirado, E. Fernandez-Garcia, S.-Y. Wu, M.D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy (IAA-CSIC), C. Perez del Pulgar (Univ. de Malaga), G. Garcia-Segura (Inst. de Astronomia, UNAM), M. Gritsevich (Univ. of Helsinki), D. R. Xiong (Yunnan Observatories of CAS), Y.-D. Hu (GuangXi Univ.), B.-B. Zhang (Nanjing Univ.) and A. Maury (Space, San Pedro de Atacama), on behalf of a larger collaboration, report: Following the detection of EP 250427a by EP (Wang et al., GCNC 40257), the 0.6m BOOTES-7 robotic telescope at San Pedro de Atacama (Chile) automatically responded to this fast X-ray transient starting on Apr 27, 07:21:09 UT (i.e., ~4 hours after detection). In the first 60 s exposure image, an uncatalogued source is detected at the EP-FXT position, at coordinates (J2000): RA = 18:29:05.7, Dec = +07:33:46.5, with a preliminary magnitude of 18.1 +/- 0.08 mag (clear filter) using GaiaDR3 Gmag as a reference, which we propose to be the optical afterglow to EP 250427a. Spectroscopic observations are encouraged. We thank the staff at San Pedro de Atacama Celestial Observations for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/40259. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38287] EP250427a: Global MASTER-Net observations report
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40258 SUBJECT: EP250427a: Global MASTER-Net observations report DATE: 25/04/27 10:09:47 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP250427a ( EP Team et al., GCN 40257) errorbox 254 sec after notice time and 21870 sec after trigger time at 2025-04-27 09:43:15 UT, with upper limit up to 18.4 mag. The observations began at zenith distance = 41 deg. The sun altitude is -17.5 deg. The galactic latitude b = 8 deg., longitude l = 37 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2854486 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 21901 | 2025-04-27 09:43:15 | MASTER-OAFA | (18h 28m 05.12s , +07d 20m 04.3s) | C | 60 | 18.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40258. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38286] EP250427a: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40257 SUBJECT: EP250427a: Einstein Probe detection of a fast X-ray transient DATE: 25/04/27 09:34:46 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.Wang (PMO, CAS), D. Y. Li (NAO, CAS), Y. Q. Zhao (USTC, PRIC), J. H. Wu (GZHU), Y, Liu (NAO, CAS) 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 EP250427a (GCN Notice ID 01709135324). The WXT position of the source is R.A. = 277.281 deg, DEC = 7.570 deg (J2000) with an uncertainty of 2.0 arcmin in radius (90% C.L. statistical and systematic). A preliminary analysis of the EP-WXT data shows that the transient began at 2025-04-27T03:38:45(UTC) (before which the satellite was in the SAA region, and the real start time might be earlier than the value reported here) and lasted for about 180s, with a peak flux of 2 x 10^-8 erg/cm^2/s. The averaged WXT spectrum can be fitted by an absorbed power law model with a photon index of 1.70 (+0.36, -0.34) and a column density of 3.92 (+0.14, -0.13) x 10^21 cm^-2. The unabsorbed 0.5-4 keV flux is about 1.96 (+0.31, -0.23) x 10^-9 erg/cm^2/s. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed about 5 hours after the WXT detection. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 277.2746 deg, DEC = 7.5639 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 is received. The contact TA of EP250427a is Y. Wang. Please contact him via email wangyun(a)pmo.ac.cn if needed. 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/40257. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38285] IceCube Alert 250426.74: Global MASTER-Net observations report
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40256 SUBJECT: IceCube Alert 250426.74: Global MASTER-Net observations report DATE: 25/04/27 00:27:01 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 (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the IceCube Alert 250426.74 (trigger No 52432631,19h 45m 04.08s , +20d 41m 27.6s, R=0.56) errorbox 23060 sec after notice time and 23122 sec after trigger time at 2025-04-27 00:10:20 UT, with upper limit up to 17.5 mag. The observations began at zenith distance = 76 deg. The sun altitude is -61.8 deg. The galactic latitude b = -2 deg., longitude l = 58 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2853923 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 23152 | 2025-04-27 00:10:20 | MASTER-SAAO | (19h 42m 54.59s , +20d 09m 14.4s) | C | 60 | 17.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40256. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38284] GRB 250424A: Swift-BAT refined analysis
by GCN Circulars 26 Apr '25

26 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40255 SUBJECT: GRB 250424A: Swift-BAT refined analysis DATE: 25/04/26 22:48:38 GMT FROM: Rahul Gupta at NASA GSFC <rahul.gupta(a)nasa.gov> C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC), S. B. Cenko (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), 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-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250424A (trigger #1306404) (Cenko, et al., GCN Circ. 40224). The BAT ground-calculated position is RA, Dec = 217.528, -35.025 deg which is RA(J2000) = 14h 30m 06.7s Dec(J2000) = -35d 01' 30.6" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 39%. The mask-weighted BAT light curve of the burst (began during a slew) shows a faint precursor emission followed by a bright main pulse. T90 (15-350 keV) is 19.03 +- 1.06 sec (estimated error including systematics), with the T90 starting at T0-20.76 sec due to the slew-delayed T0. The time-averaged spectrum from T-38.75 to T+262.67 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.54 +- 0.13, and Epeak of 106.5 +- 33.7 keV (chi squared 47.05 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 3.2 +- 0.1 x 10^-05 erg/cm2 and the 1-sec peak flux measured from T-15.38 sec in the 15-150 keV band is 47.0 +- 1.3 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.79 +- 0.03 (chi squared 58.54 for 57 d.o.f.). 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/1306404 View this GCN Circular online at https://gcn.nasa.gov/circulars/40255. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38283] IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 26 Apr '25

26 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40254 SUBJECT: IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/04/26 19:17:00 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 25-04-26 at 17:44:58.16 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 2.2610 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/140843_52432631.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 25-04-26 Time: 17:44:58.16 UT RA: 296.37 (+0.53/-0.50 deg 90% PSF containment) J2000 Dec: 20.7 (+0.52/-0.52 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/40254. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38282] IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 26 Apr '25

26 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40253 SUBJECT: IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/04/26 19:16:27 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 25-04-26 at 17:44:58.16 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 2.2610 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/140843_52432631.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 25-04-26 Time: 17:44:58.16 UT RA: 296.37 (+0.53/-0.50 deg 90% PSF containment) J2000 Dec: 20.7 (+0.52/-0.52 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/40253. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38281] GRB 250424A: SVOM/GRM observation of a long burst
by GCN Circulars 26 Apr '25

26 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40252 SUBJECT: GRB 250424A: SVOM/GRM observation of a long burst DATE: 25/04/26 13:30:39 GMT FROM: zhangjinpeng(a)ihep.ac.cn SVOM/GRM team: Jin-Peng Zhang, Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Jean-Luc Atteia (IRAP), Olivier Godet (IRAP), Stéphane Schanne (CEA), Frédéric Daigne (IAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 250424A (SVOM trigger reference: sb25042401) at 2025-04-24T06:52:08.000 (T0). This burst was also detected by Swift (Cenko et al., GCN 40224), AstroSat CZTI (Harsha et al., GCN 40231), Konus-Wind (Ridnaia et al., GCN 40243) and EIRSAT-1 GMOD (McKenna et al., GCN 40249). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-pulses with a T90 of 18.8 +1.0/-1.0 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250424A.png In addition, the position of this burst, as determined by Swift (Cenko et al., GCN 40224, RA: 217.50010 deg, DEC: -35.02493 deg, Error: 1.9 arcseconds), is located at about 63.7 degrees from the SVOM optical axis, and outside the ECLAIRs field of view. The time-averaged spectrum from T0-5 to T0+18 s is best fitted by Band function. The alpha is -1.14 +/- 0.06, the beta is -2.44 +/- 0.08, and the cutoff energy, parameterized as Epeak, is 89 +/- 5 keV. The event fluence (10-1000 keV) in this time interval is (6.63 +/- 0.12)E-05 erg/cm^2. With a redshift of 0.310 (Saccardi et al., GCN 40228), GRB 250424A is consistent with Type II GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/grb250424A_amati.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/GRM point of contact for this burst is: Jin-Peng Zhang (IHEP) (zhangjinpeng(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/40252. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38280] GRB 250424A: PRIME near-infrared detection
by GCN Circulars 26 Apr '25

26 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40251 SUBJECT: GRB 250424A: PRIME near-infrared detection DATE: 25/04/26 00:30:37 GMT FROM: O. Guiffreda at UMD <oriogui(a)umd.edu> M. Elkabir (U Rome), O. Guiffreda (UMD), J. Durbak (UMD), N. Passaleva (U Rome), E. Troja (U Rome), A. S. Kutyrev (NASA/GSFC), S. B. Cenko (NASA/GSFC) Following the Swift BAT detection (GCN 40224), we observed the transient field in J and H filters with PRIME ~12 hours after the initial Swift detection. At the position of the optical counterpart reported by Swift UVOT (GCN 40244), we detect an uncatalogued source in both J and H band. Using nearby VISTA Hemispherical Survey (VHS) for preliminary calibration we derive the following magnitudes and limits, not corrected for Galactic extinction: |Filter | Mag(AB) | |-------|---------------| |J | 18.8 +/- 0.06 | |H | 19.2 +/- 0.05 | 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/40251. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38279] GRB 250424A: WINTER J-band detection
by GCN Circulars 25 Apr '25

25 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40250 SUBJECT: GRB 250424A: WINTER J-band detection DATE: 25/04/25 20:51:47 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> Benjamin Schneider (LAM), Geoffrey Mo (MIT), Tomas Ahumada (Caltech), Viraj Karambelkar (Caltech), Danielle Frostig (CfA), Robert Stein (UMD), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the GRB 250424A (Cenko et al., GCN 40224; Harsha et al., GCN 40231; Ridnaia et al., GCN 40243) in the near-infrared with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations started on 2025-04-24 at 07:33:24 UT (40.92 min after the Swift trigger) and consisted of 15 exposures of 120 s in the J-band. In the stacked image, we detect the optical counterpart reported by Cenko et al., GCN 40224; Brivio et al., GCN 40225; Becerra et al., GCN 40226; Saccardi et al., GCN 40228; de Wet et al., GCN 40229; Ducoin et al., GCN 40230; Turpin et al., GCN 40240, Dutton et al., GCN 40241; Siegel et al., GCN 40244. The preliminary AB magnitude derived for that source is: J = 18.1 +/- 0.2 The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565). The photometric calibration was performed using nearby stars from the 2MASS catalog and the magnitude is not corrected for Galactic extinction. WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/40250. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38278] GRB 250424A: EIRSAT-1 GMOD Detection
by GCN Circulars 25 Apr '25

25 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40249 SUBJECT: GRB 250424A: EIRSAT-1 GMOD Detection DATE: 25/04/25 20:36:05 GMT FROM: Caimin McKenna at University College Dublin <caimin.mckenna(a)ucdconnect.ie> C. McKenna, P. McDermott, D. Murphy, C. de Barra, A. Ulyanov, G. Finneran, G. Corcoran, L. Cotter, A. Empey, J. Fisher, F. Gibson Kiely, J. Thompson, D. McKeown, A. Martin-Carrillo, L. Hanlon, S. McBreen, on behalf of the EIRSAT-1 team: EIRSAT-1 reports the detection of the long gamma-ray burst GRB 250424A by the Gamma-ray Module (GMOD) instrument, which was also detected by Swift-BAT (GCN [40224](https://gcn.nasa.gov/circulars/40224)), Calet/CGBM (Trigger No. 1429512582), AstroSat CZTI (GCN [40231](https://gcn.nasa.gov/circulars/40231)), and Konus-Wind (GCN [40243](https://gcn.nasa.gov/circulars/40243)). The GMOD detection was made starting at 2025-04-24 06:52:12.6 UTC. The GMOD light curve for GRB 250424A, with 1.2s binning, shows a long, smooth, single pulse, consistent with other observations. The spacecraft location at time of detection was 23.407 S, 123.088 W and an altitude of 402.9 km. The light curve for this event as measured by GMOD can be found here: https://grb.eirsat1.ie/250424A/250424A_LC_onboard_preliminary.png EIRSAT-1 is Ireland’s first satellite (Doyle et al. Proceedings of the 4th SSEA, 2022). It is a 2U CubeSat and carries onboard a number of experiments including the Gamma-Ray Module (GMOD), a novel, compact, gamma-ray detector (Murphy et al, Experimental Astronomy, 53, 961–990, 2022). GMOD consists of a 25 mm × 25 mm × 40 mm Cerium Bromide scintillator coupled to SiPMs and is designed to detect gamma-ray bursts in the ~ 60 keV - 1.5 MeV range. EIRSAT-1 was developed in University College Dublin with support from ESA’s Fly Your Satellite! programme and was launched on 1st December 2023. View this GCN Circular online at https://gcn.nasa.gov/circulars/40249. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38277] IceCube-250416A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 25 Apr '25

25 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40248 SUBJECT: IceCube-250416A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/04/25 14:19:46 GMT FROM: Jessie Thwaites at IceCube/U Wisc-Madison <thwaites(a)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-250416A (https://gcn.nasa.gov/circulars/40153) in a time range of 1000 seconds centered on the alert event time (2025-04-16 18:23:54.970 UTC to 2025-04-16 18:40:34.970 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-250416A. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250416A is 1.4e-01 GeV cm^-2 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 1e+05 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2025-04-15 18:32:14.970 UTC to 2025-04-17 18:32:14.970 UTC). In this case, we report a p-value of 0.39, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250416A is 1.6e-01 GeV cm^-2 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/40248. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38276] IceCube-250421A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 25 Apr '25

25 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40247 SUBJECT: IceCube-250421A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/04/25 14:18:59 GMT FROM: Jessie Thwaites at IceCube/U Wisc-Madison <thwaites(a)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-250421A (https://gcn.nasa.gov/circulars/40195) in a time range of 1000 seconds centered on the alert event time (2025-04-21 16:57:48.070 UTC to 2025-04-21 17:14:28.070 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-250421A. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250421A is 1.4e-01 GeV cm^-2 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 7e+04 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2025-04-20 17:06:08.070 UTC to 2025-04-22 17:06:08.070 UTC). In this case, we report a p-value of 0.26, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250421A ranges from 1.6e-01 to 1.7e-01 GeV cm^-2 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/40247. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38275] GRB 250424A: SVOM/VT optical observation
by GCN Circulars 25 Apr '25

25 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40246 SUBJECT: GRB 250424A: SVOM/VT optical observation DATE: 25/04/25 11:38:33 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Z.H. Yao(NAOC), X. H. Han(NAOC), Y. D. Hu(GXU),L. Zhang(IHEP), X. L. Chen(YNU), L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. Xu, P. P. Zhang, W. J. Xie, J. Wang, Y. J. Xiao, H. B. Cai, L. Lan, J. Y. Wei (NAOC) report on behalf of the SVOM mission team. SVOM/VT conducted ToO follow-up observations of the GRB 250424A(Francile et al., GCN 40222). The observation started on 2025 Apr 24 09:26:29 UT in VT_B(400nm-650nm) and VT_R (650nm-1000nm)channel simultaneously. The candidate(Francile et al., GCN 40222; Cenko et al., GCN 40224; Brivio et al., GCN 40225; Becerra et al., GCN 40226; Saccardi et al., GCN 40228; de Wet et al., GCN 40229; Ducoin et al., GCN 40230; D. Turpin et al., GCN 40240; Dutton et al., GCN 40241; and Siegel et al., GCN 40244) was clearly detected in stacked images of both channels. The brightness in AB magnitude was estimated to be: Mid time (hour) | Band | Exposure Time (second) | Magnitude | Magnitude error 2.98 | VT_B | 60x50 | 19.89 | 0.03 2.98 | VT_R | 60x50 | 18.96 | 0.02 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. 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/40246. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38274] GRB 250419A: Mondy Optical Observations
by GCN Circulars 25 Apr '25

25 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40245 SUBJECT: GRB 250419A: Mondy Optical Observations DATE: 25/04/25 07:34:22 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP) report on behalf of IKI-GRB-FuN: We continued observations of the field of GRB 250419A (Wang et al., GCN 40168; Page et al., GCN 40111; Page et al., GCN 40176) at the redshift of z = 0.845 (Thakur et al., GCN 40174) with the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy). The R-band observations began on 2025-04-22 at 17:29:31 UT, i.e. ~3.65 days since trigger. The field of the optical counterpart was observed by (López et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172; Thakur et al., GCN 40174; Lipunov et al., GCN 40179; Odeh et al., GCN 40180; Perley & Bochenek, GCN 40181; Pankov et al., GCN 40182; Pérez-Fournon et al., GCN 40183; Kuin, GCN 40185; Wu et al., GCN 40186; Xie et al., GCN 40187; Jiang et al., GCN 40188; Ghosh et al., GCN 40189; Bochenek & Perley, GCN 40190; Pankov et. al, GCN 40202; Masi, GCN GCN 40206; Calapai, GCN 40209; Lagioia et al., GCN 40210; Dimple & Gompertz, GCN 40238; Bochenek & Perley, GCN 40239). We detect the OT in the stacked image. The preliminary photometry is as follows: Date UTstart Exptime t-T0 Filter OT Err UL (s) (mid, days) (3sigma) 2025-04-22 17:29:31 45*120 3.65625 R 21.83 0.15 22.5 The photometry is based on nearby USNO-B1.0 stars (R2 magnitudes, provided in Pankov et al., GCN 40182) and has not been corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40245. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38273] GRB 250424A: Swift/UVOT Detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40244 SUBJECT: GRB 250424A: Swift/UVOT Detection DATE: 25/04/24 23:09:21 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M.H. Siegel (PSU) and S. B. Cenko (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250424A 254 s after the BAT trigger (Cenko et al., GCN Circ. 40224). A source consistent with the XRT position (Evans et al., GCN Circ. 40232) and the optical transient (Francile et al., GCN Circ. 40222, Brivio et al., GCN Circ. 40225; Becerra et al., GCN Circ. 40226; de Wet et al., GCN Circ. 40229; Ducoin et al., GCN Circ. 40230; Turpin et al., GCN Circ. 40240; Dutton et al., GCN Circ. 40241) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 14:29:60.00 = 217.49998 (deg.) Dec (J2000) = -35:01:30.6 = -35.02518 (deg.) with an estimated uncertainty of 0.47 arc sec. (radius, 90% confidence). Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 254 404 147 18.96 +/- 0.07 v 411 1918 175 >18.7 b 509 1844 136 19.97 +/- 0.26 u 485 1647 136 19.15 +/- 0.20 w1 460 1795 156 19.44 +/- 0.31 m2 436 1598 97 >18.4 w2 559 1894 156 >19.9 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.064 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40244. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38272] Konus-Wind detection of GRB 250424A
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40243 SUBJECT: Konus-Wind detection of GRB 250424A DATE: 25/04/24 22:12:37 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB GRB 250424A (Swift-BAT detection: Cenko et al., GCN 40224; AstroSat CZTI detection: Harsha et al., GCN 40231) triggered Konus-Wind at T0=24733.431 s UT (06:52:13.431). The burst light curve shows a single pulse which starts at ~T0-17.9 s and has a total duration of ~40.5 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/GRB250424_T24733/ As observed by Konus-Wind, the burst had a fluence of 5.83(-0.16,+0.16)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+4.192 s, of 8.88(-0.94,+0.95)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+21.760 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.30(-0.06,+0.06), the high energy photon index beta = -2.87(-0.15,+0.11), the peak energy Ep = 104(-3,+3) keV (chi2 = 94/82 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+5.376 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.09(-0.06,+0.07), the high energy photon index beta = -2.91(-0.15,+0.12), the peak energy Ep = 129(-4,+5) keV (chi2 = 72/66 dof). Assuming the redshift z=0.310 (Saccardi et al., GCN 40228) 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 following rest-frame parameters: the isotropic energy release E_iso is 1.49(-0.04,+0.04)x10^52 erg, the peak luminosity L_iso is 2.97(-0.31,+0.32)x10^51 erg/s, the rest-frame peak energy of the time-averaged spectrum Ep,i,z is 137(-4,+4) keV and the spectrum near the maximum count rate Ep,p,z is 169(-5,+7) keV. With the obtained estimates, GRB 250424A is inside 68% prediction bands for both 'Amati' and 'Yonetoku' relations derived 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/GRB250424_T24733/GRB250424A_rest_frame.pdf All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/40243. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38271] Konus-Wind detection of GRB 250424A
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40243 SUBJECT: Konus-Wind detection of GRB 250424A DATE: 25/04/24 22:12:37 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB GRB 250424A (Swift-BAT detection: Cenko et al., GCN 40224; AstroSat CZTI detection: Harsha et al., GCN 40231) triggered Konus-Wind at T0=24733.431 s UT (06:52:13.431). The burst light curve shows a single pulse which starts at ~T0-17.9 s and has a total duration of ~40.5 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/GRB250424_T24733/ As observed by Konus-Wind, the burst had a fluence of 5.83(-0.16,+0.16)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+4.192 s, of 8.88(-0.94,+0.95)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+21.760 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.30(-0.06,+0.06), the high energy photon index beta = -2.87(-0.15,+0.11), the peak energy Ep = 104(-3,+3) keV (chi2 = 94/82 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+5.376 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.09(-0.06,+0.07), the high energy photon index beta = -2.91(-0.15,+0.12), the peak energy Ep = 129(-4,+5) keV (chi2 = 72/66 dof). Assuming the redshift z=0.310 (Saccardi et al., GCN 40228) 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 following rest-frame parameters: the isotropic energy release E_iso is 1.49(-0.04,+0.04)x10^52 erg, the peak luminosity L_iso is 2.97(-0.31,+0.32)x10^51 erg/s, the rest-frame peak energy of the time-averaged spectrum Ep,i,z is 137(-4,+4) keV and the spectrum near the maximum count rate Ep,p,z is 169(-5,+7) keV. With the obtained estimates, GRB 250424A is inside 68% prediction bands for both 'Amati' and 'Yonetoku' relations derived 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/GRB250424_T24733/GRB250424A_rest_frame.pdf All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/40243. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38270] Fermi-LAT gamma-ray observations of IceCube-250421A
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40242 SUBJECT: Fermi-LAT gamma-ray observations of IceCube-250421A DATE: 25/04/24 20:30:21 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg), S. Garrappa (Weizmann Institute of Science) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the IC250421A high-energy neutrino event (GCN 40195) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 25-04-21 at 17:06:08.07 UT (T0) with J2000 position RA = 240.91 (+2.62, -4.44) deg, Decl. = +28.67 (+1.70, -1.70) deg (90% PSF containment). There are five catalogued gamma-ray sources (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546) located within the 90% IC250421A localization region. These are: 4FGL J1606.5+2717, associated with B2 1604+27; 4FGL J1556.1+2812, associated with NVSS J155611+281134; 4FGL J1612.2+2828, associated with TXS 1610+285; 4FGL J1545.5+2839, associated with WISEA J154520.76+283508.6; 4FGL J1555.3+2903 (unassociated). Based on a preliminary analysis of the LAT data over the timescale of one day and one month prior T0, these objects are not significantly detected at gamma-rays. We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) at the IC250421A bestfit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC250421A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.21 e-10 ph cm^-2 s^-1 for ~16-years (2008-08-04 / T0), < 4.61e-09 (<1.01e-07) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Within the error circle for the direction of the neutrino, 1.39 deg offset from the best-fitIC250421 position, a ~14 sigma excess of gamma rays, Fermi J1605.3+2959, was detected in an analysis of the integrated LAT data (0.1 - 300 GeV) between 2008-08-04 and T0. Assuming a power-law spectrum, the candidate gamma-ray source has best-fit localization of RA = 241.39 deg, Dec = +30.00 deg (0.16 deg 99% containment, 0.13 deg 95% containment, 0.08 deg 68% containment) with best fit spectral parameters flux = (1.20± 0.12) × 10^-8 ph cm^-2 s^-1, index = 3.18 ± 0.23. A possible counterpart for Fermi J1605.3+2959 is the FSRQ CGRaBS J1605+3001 (a.k.a. BZQ J1605+3001, Stephen E. & Healey et al 2007, ApJS, 171, 61) with a redshift of 2.41 (Sloan Digital Sky Survey 2017, ApJS, 233, 25), located at 0.03 deg from the Fermi J1605.3+2959 best-fit position, within the 68% localization error. A preliminary analysis of the temporal variability at the position of Fermi J1605.3+2959 reveals that the source underwent an approximately six-months long period of enhanced activity between late 2023 and early 2024. In addition, in a preliminary analysis of the LAT data over 1-month timescale, we test the presence of an additional point source at the position of the optical transient SN2025cbj, a ~60-days old SN of Type-IIn which was reported in spatial coincidence with IC250421A in GCN#40208. No significant gamma-ray emission was detected. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the SN2025cbj best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.13e-08 ph cm^-2 s^-1 for a 1-month integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this region will continue. For these observations the Fermi-LAT contact person is L. Pfeiffer (leonard.pfeiffer at uni-wuerzburg.de). The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/40242. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38269] Fermi-LAT gamma-ray observations of IceCube-250421A
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40242 SUBJECT: Fermi-LAT gamma-ray observations of IceCube-250421A DATE: 25/04/24 20:30:21 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg), S. Garrappa (Weizmann Institute of Science) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the IC250421A high-energy neutrino event (GCN 40195) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 25-04-21 at 17:06:08.07 UT (T0) with J2000 position RA = 240.91 (+2.62, -4.44) deg, Decl. = +28.67 (+1.70, -1.70) deg (90% PSF containment). There are five catalogued gamma-ray sources (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546) located within the 90% IC250421A localization region. These are: 4FGL J1606.5+2717, associated with B2 1604+27; 4FGL J1556.1+2812, associated with NVSS J155611+281134; 4FGL J1612.2+2828, associated with TXS 1610+285; 4FGL J1545.5+2839, associated with WISEA J154520.76+283508.6; 4FGL J1555.3+2903 (unassociated). Based on a preliminary analysis of the LAT data over the timescale of one day and one month prior T0, these objects are not significantly detected at gamma-rays. We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) at the IC250421A bestfit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC250421A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.21 e-10 ph cm^-2 s^-1 for ~16-years (2008-08-04 / T0), < 4.61e-09 (<1.01e-07) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Within the error circle for the direction of the neutrino, 1.39 deg offset from the best-fitIC250421 position, a ~14 sigma excess of gamma rays, Fermi J1605.3+2959, was detected in an analysis of the integrated LAT data (0.1 - 300 GeV) between 2008-08-04 and T0. Assuming a power-law spectrum, the candidate gamma-ray source has best-fit localization of RA = 241.39 deg, Dec = +30.00 deg (0.16 deg 99% containment, 0.13 deg 95% containment, 0.08 deg 68% containment) with best fit spectral parameters flux = (1.20± 0.12) × 10^-8 ph cm^-2 s^-1, index = 3.18 ± 0.23. A possible counterpart for Fermi J1605.3+2959 is the FSRQ CGRaBS J1605+3001 (a.k.a. BZQ J1605+3001, Stephen E. & Healey et al 2007, ApJS, 171, 61) with a redshift of 2.41 (Sloan Digital Sky Survey 2017, ApJS, 233, 25), located at 0.03 deg from the Fermi J1605.3+2959 best-fit position, within the 68% localization error. A preliminary analysis of the temporal variability at the position of Fermi J1605.3+2959 reveals that the source underwent an approximately six-months long period of enhanced activity between late 2023 and early 2024. In addition, in a preliminary analysis of the LAT data over 1-month timescale, we test the presence of an additional point source at the position of the optical transient SN2025cbj, a ~60-days old SN of Type-IIn which was reported in spatial coincidence with IC250421A in GCN#40208. No significant gamma-ray emission was detected. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the SN2025cbj best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.13e-08 ph cm^-2 s^-1 for a 1-month integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this region will continue. For these observations the Fermi-LAT contact person is L. Pfeiffer (leonard.pfeiffer at uni-wuerzburg.de). The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/40242. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38268] GRB 250424A: Skynet Optical Observations
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40241 SUBJECT: GRB 250424A: Skynet Optical Observations DATE: 25/04/24 20:17:01 GMT FROM: Dylan Dutton at UNC Chapel Hill <ddutton59(a)gmail.com> Dylan Dutton, Daniel Reichart, Joshua Haislip, Vladimir Kouprianov, and Donovan Schlekat report on behalf of the Skynet Robotic Telescope Network at the University of North Carolina at Chapel Hill. We observed the field of GRB 250424A detected by Swift (Cenko, GCN 40224) with one of Skynet's PROMPT telescopes located at the Cerro Tololo Inter-American Observatory. We detect the optical afterglow (Francile et al., GCN 40222; Cenko et al., GCN 40224; Brivio et al., GCN 40225; Becerra et al., GCN 40226; Saccardi et al., GCN 40228; de Wet et al., GCN 40229; Ducoin et al., GCN 40230; and D. Turpin et al., GCN 40240) in the B, V, and R bands and report the initial photometry below. Exposure lengths were calculated using our automated exposure length scaling model. Tmid - T0 (s)| Telescope | Filter | Exposure (s) | Mag | Mag Error ------------------------------------------------------------------ 1224 | PROMPT-5 | B | 264 | 19.610 | 0.054 1467 | PROMPT-5 | V | 216 | 19.253 | 0.065 1649 | PROMPT-5 | R | 144 | 18.500 | 0.051 Our images have been calibrated using stars from the APASS catalog. Magnitudes were not corrected for dust extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40241. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38267] GRB 250424A: Kilonova-Catcher optical afterglow detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40240 SUBJECT: GRB 250424A: Kilonova-Catcher optical afterglow detection DATE: 25/04/24 18:25:31 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> D. Turpin (CEA-Saclay/Irfu), R. Hellot, P. Jaquiery, M. Freeberg (KNC), C. Andrade(UMN), S. Antier (OCA), M. Coughlin (UMN),S. Karpov (FZU), I. Tosta e Melo (UniCT-DFA), P. Hello (IJCLAB), P-A Duverne (APC), T. Pradier (Unistra/IPHC), N. Guessoum (AUS), M. Pillas (ULiege) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 250424A (Cenko et al., GCN 40224) detected by Swift/BAT with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the iT30 telescope at the Siding Spring Observatory, a Celestron C14 telescope at Beverly Begg Observatory (New Zealand) and a CDK17 telescope located at AITP San Pedro Chile Observatory starting from TGRB+1.3hr. In our stacked frames, subtracted from the Legacy Survey DR10 template image, we detect the optical afterglow at the position reported by Swift/UVOT (Cenko et al., GCN 40224), REM (Brivio et al., GCN 40225), DDOTI (Becerra et al., GCN 40226), VLT/X-Shooter (Saccardi et al., GCN 40228), BlackGEM (de Wet et al., GCN 40229)and COLIBRI (Ducoin et al., GCN 40230). We report some of our detections in the table below: +---------------+-----------+-----------+----------------+------------+ | Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument | +===============+===========+===========+================+============+ | 1.3 | 1 x 300s | r (AB) | 19.34 +/- 0.09 | CDK17-AITP | | 4.0 | 20 x 120s | r (AB) | 19.74 +/- 0.07 | C14-BBO | | 6.8 | 17 x 180s | Rc (Vega) | 19.95 +/- 0.09 | iT30 | +---------------+-----------+-----------+----------------+------------+ All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained in Johnson Cousin filters were calibrated using the Gaia DR3 Synphot catalog while the sloan images were calibrated using the SkyMapper DR4 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/40240. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38266] GRB 250419a: Continued Liverpool Telescope observations
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40239 SUBJECT: GRB 250419a: Continued Liverpool Telescope observations DATE: 25/04/24 16:42:10 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 have been regularly observing the optical afterglow of SVOM-detected GRB250419a (Wang et al., GCN 40168, Brunet et al. GCN 40234), first reported by López et al. (GCN 40169) and Xin et al. (GCN 40170), using the IO:O optical camera on the 2m robotic Liverpool Telescope in the SDSS r and i filters. Observations began on 2025-04-19 (Perley & Bochenek, GCN 40181) and have continued nightly since. The most recent set of observations was a set of 8x100s exposures starting at 2025-04-23 21:52:15 UT, approximately 4.86 days after the trigger. We report a detection, given below, in both bands. MJD (mid) T_mid-T_0 Filter Mag. (AB) 60788.97067 4.86 d r 23.20 ± 0.27 60788.98199 4.87 d i 22.91 ± 0.22 The photometry was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. The magnitudes are consistent with the upper limit from earlier in the night reported by Gompertz et al. (GCN 40238). The source is currently fading rapidly: a fit to our observations taken 2 days and later after the trigger gives a power-law decay index of approximately -2.1, consistent with a post-jet-break evolution. View this GCN Circular online at https://gcn.nasa.gov/circulars/40239. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38265] GRB 250419A: Liverpool Telescope optical upper limit
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40238 SUBJECT: GRB 250419A: Liverpool Telescope optical upper limit DATE: 25/04/24 15:05:29 GMT FROM: Dimple at University of Birmingham <dimplepanchal96(a)gmail.com> Dimple and B. P. Gompertz (U. Birmingham) report: We conducted follow-up observations of GRB 250419A (Wang et al., GCN 40168) with the IO:O camera on the 2m robotic Liverpool Telescope (LT). Observations began at 21:52:15.745 UT on 2025-04-23 and consisted of 5x120 s exposures in each of the SDSS g and r filters. We do not detect the optical afterglow (López et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172; Thakur et al., GCN 40174; Lipunov et al., GCN 40179; Odeh et al., GCN 40180; Perley & Bochenek, GCN 40181; Pankov et al., GCN 40182; Pérez-Fournon et al., GCN 40183; Kuin et al., GCN 40185; Wu et al., GCN 40186; Xie et al., GCN 40187; Jiang et al., GCN 40188; Ghosh et al., GCN 40189; Bochenek & Perley, GCN 40190; Pankov et al., GCN 40202; Masi, GCN 40206; Calapai, GCN 40209) to 3-sigma limiting AB magnitudes of g > 22.42 and r >22.45, at a mid-time of 4.82 days after trigger. Observations were calibrated against nearby Pan-STARRS stars and are not corrected for foreground extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40238. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38264] GRB 250407A: GRBAlpha detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40237 SUBJECT: GRB 250407A: GRBAlpha detection DATE: 25/04/24 15:03:43 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), N. Husarikova, F. Munz , M. Topinka, M. Duriskova, M. Kolar, L. Szakszonova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration. The long-duration GRB 250407A (Fermi/GBM detection: GCN 40104; SVOM/GRM detection: GCN 40120; Wind/Konus detection: GCN 40121) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract). The detection was confirmed at the peak time 2025-04-07 15:48:21.6 UTC. The T90 duration measured by GRBAlpha is 2.0 s and the overall significance during T90 reaches 42 sigma. We note that GRBAlpha was passing through the van Allen radiation belt at the time of this burst and thus experienced a higher background. The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250407A_GCN.pdf All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/ GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume. View this GCN Circular online at https://gcn.nasa.gov/circulars/40237. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38263] GRB 250404A / EP250404a: GRBAlpha detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40236 SUBJECT: GRB 250404A / EP250404a: GRBAlpha detection DATE: 25/04/24 15:03:18 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), N. Husarikova, F. Munz , M. Topinka, M. Duriskova, M. Kolar, L. Szakszonova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration. The long-duration GRB 250404A / EP250404a (Fermi/GBM detection: GCN 40050; EP/WXT detection: GCN 40051; Wind/Konus detection: GCN 40087) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract). The detection was confirmed at the peak time 2025-04-04 14:20:37.4 UTC. The T90 duration measured by GRBAlpha is 67 s and the overall significance during T90 reaches 19 sigma. The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250404A_GCN.pdf All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/ GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume. View this GCN Circular online at https://gcn.nasa.gov/circulars/40236. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38262] GRB 250330B: GRBAlpha detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40235 SUBJECT: GRB 250330B: GRBAlpha detection DATE: 25/04/24 14:56:21 GMT FROM: Jakub Ripa <ripa.jakub(a)gmail.com> J. Ripa, M. Dafcikova (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), N. Husarikova, F. Munz, M. Topinka, M. Duriskova, M. Kolar, L. Szakszonova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration. The short-duration GRB 250330B (Fermi/GBM detection: GCN 39951; EIRSAT-1/GMOD detection: GCN 39989; SVOM/GRM detection: GCN 39993; Wind/Konus detection trigger at 2025-03-30 21:52:22.793 UTC) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract). The detection was confirmed at the peak time 2025-03-30 21:52:21.7 UTC. The T90 duration measured by GRBAlpha is 1.0 s and the overall significance during T90 reaches 6.8 sigma. The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250330B_GCN.pdf All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/ GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume. View this GCN Circular online at https://gcn.nasa.gov/circulars/40235. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38261] GRB 250419A: SVOM/ECLAIRs refined analysis
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40234 SUBJECT: GRB 250419A: SVOM/ECLAIRs refined analysis DATE: 25/04/24 14:12:58 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet (IRAP), M. G. Bernardini (INAF-OAB, LUPM), A. Coleiro, F. Cangemi (APC), O. Godet (IRAP), W. J. Xie, D. H. ZHAO (NAO, CAS), B.-T. Wang (YNAO, CAS), Y. H. Cheng (SWIFAR,YNU) Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250419A (SVOM burst-id sb25041901). The burst that triggered ECLAIRs onboard (GCN 40168) consists of a single pulse with a duration of T90 = 11.44 -2.58/+2.85 s in the 5-8 keV energy band. However, the full dataset shows another pulse with a duration of ~15 s at ~Tb-120 s. No counts are detected above 12 keV for the first pulse and above 10 keV for the second one, making this event very soft. The time-averaged spectrum of the first pulse (from Tb-118s to Tb-102s) in the energy range 4-12 keV is best fit by a simple power-law model with a photon index 3.01 -0.69/+0.80. The time-averaged spectrum of the second pulse (from Tb to Tb+20s) in the energy range 4-10 keV is best fit by a simple power-law model with a photon index 3.02 -0.53/+0.56. The total fluence in the 4-10 keV band is (1.41 -0.37/+0.03) e-7 erg/cm^2. In both time intervals, a black-body model (zbb model in Xspec with z = 0.845, GCN 40174) provides an adequate fit to the data. The first pulse has a temperature of 2.44 -0.54/+0.64 keV, and the second one a temperature of 2.28 - 0.31/+0.38 keV. In that case, the total fluence is (1.38 0.10/+0.06) e-7 erg/cm^2. All the quoted errors are at the 90% confidence level. The spectral fits suggest that the Epeak of this burst is below the ECLAIRs energy range, i.e. <4 keV. Therefore this burst could be classified as an X-Ray Flash (XRF). 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/40234. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38260] GRB 250424A: Swift-XRT refined Analysis
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40233 SUBJECT: GRB 250424A: Swift-XRT refined Analysis DATE: 25/04/24 13:59:17 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU), M. A. Williams (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.9 ks of XRT data for GRB 250424A, from 259 s to 18.9 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=0.20 (+0.12, -0.13). At T+2382 s the decay steepens to an alpha of 0.53 (+0.16, -0.11) before breaking again at T+17.4 ks to a final decay with index alpha=4.5 (+3.5, -2.8). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.05 (+/-0.11). The best-fitting absorption column is 1.04 (+0.11, -0.10) x 10^22 cm^-2, in excess of the Galactic value of 6.4 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 4.9 x 10^-11 (9.6 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.04 (+0.11, -0.10) x 10^22 cm^-2 Galactic foreground: 6.4 x 10^20 cm^-2 Excess significance: 15.7 sigma Photon index: 2.05 (+/-0.11) If the light curve continues to decay with a power-law decay index of 4.5, the count rate at T+24 hours will be 5.3 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.6 x 10^-14 (5.1 x 10^-14) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01306404. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40233. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38259] GRB 250424A: Enhanced Swift-XRT position
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40232 SUBJECT: GRB 250424A: Enhanced Swift-XRT position DATE: 25/04/24 12:21:10 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team. Using 3429 s of XRT Photon Counting mode data and 5 UVOT images for GRB 250424A, 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 = 217.49920, -35.02504 which is equivalent to: RA (J2000): 14h 29m 59.81s Dec (J2000): -35d 01' 30.2" 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 http://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/40232. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38258] GRB 250424A: AstroSat CZTI detection of a bright long burst
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40231 SUBJECT: GRB 250424A: AstroSat CZTI detection of a bright long burst DATE: 25/04/24 11:37:06 GMT FROM: Gaurav Waratkar at IIT Bombay <gauravwaratkar(a)iitb.ac.in> Harsha K. H. (IUCAA), M. Tembhurnikar (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the ML pipeline (Abraham et al., 2021, MNRAS, 504, 3084) and the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a bright long-duration GRB 250424A which was also detected by Swift/BAT (Cenko et. al., GCN Circ. 40224), and Calet/CGBM (Trigger No. 1429512582). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-04-24 06:52:13.50 UTC. The measured peak count rate associated with the burst is 332.3 (+35.7 -27.5) counts/s above the background in the combined data of two quadrants (out of four), with a total of 2298 (+184 -190) counts. The local mean background count rate was 157.4 (+2.7 -3.0) counts/s. Using cumulative rates, we measure a T90 of 9.2 (+1.5 -1.0) s. In the preliminary analysis, we find 665 Compton events associated with this event. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-04-24 06:52:12.48 UTC. The measured peak count rate associated with the burst is 1364 (+88, -94) counts/s above the background in the combined data of all quadrants, with a total of 8511 (+491, -536) counts. The local mean background count rate was 1507 (+7, -8) counts/s. We measure a T90 of 14 (+1, -3) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/40231. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38257] GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40230 SUBJECT: GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart DATE: 25/04/24 10:48:17 GMT FROM: J.-G. Ducoin at CPPM <ducoin(a)cppm.in2p3.fr> Jean-Grégoire Ducoin (CPPM), Benjamin Schneider (LAM), Ramandeep Gill (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA/IJCLAB), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of Swift/BAT GRB 250424A (Cenko et al., GCN Circ. 40224) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico. We started observing at 2025-04-24T08:39:07 UTC (1.78h after the trigger). The data were coadded with the COLIBRÍ pipeline and analyzed in STDWeb/STDPipe (Karpov 2025), with photometric calibration against SkyMapper DR4. Our photometry is in the AB system and is not corrected for Galactic extinction. In our first 780 seconds of exposure, At the position of the optical counterpart (Francile et al. GCN Circ. 40222; Cenko et al. GCN Circ. 40224; Brivio et al. GCN Circ. 40225; Becerra et al. GCN Circ. 40226; Saccardi et al. GCN Circ. 40228; de Wet et al. GCN Circ. 40229), we detect a source with i = 18.93 +/- 0.05 Further observations and analysis are ongoing. We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40230. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38256] GRB 250424A: BlackGEM optical afterglow detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40229 SUBJECT: GRB 250424A: BlackGEM optical afterglow detection DATE: 25/04/24 09:43:29 GMT FROM: Simon de Wet at University of Cape Town <simdewet(a)gmail.com> S. de Wet (DTU), P.J. Groot (Radboud/UCT/SAAO) and P.M. Vreeswijk (Radboud) report on behalf of the BlackGEM consortium: The BlackGEM Unit Telescope 4 (BG4) located at ESO La Silla, Chile, responded automatically to the Swift trigger on GRB 250424A (Cenko et al., GCN 40224) and obtained a repeating series of 60 s exposures in the q,u,g,r,i,z bands. The first exposure started 264 s after the trigger time at 06:56:53 UT on 2025 April 24. A total of 26 exposures were obtained. We detect the optical afterglow with the following AB magnitudes: q = 18.30 +/- 0.03 at 06:57:24 UT u = 19.33 +/- 0.18 at 06:58:47 UT g = 18.98 +/- 0.05 at 07:01:32 UT r = 18.58 +/- 0.04 at 07:04:17 UT i = 18.26 +/- 0.04 at 07:07:02 UT z = 18.22 +/- 0.10 at 07:09:46 UT BlackGEM is an array of wide-field telescopes designed, built and operated by a consortium consisting of Radboud University, the Netherlands Research School for Astronomy NOVA, KU Leuven, the University of Manchester, Tel Aviv University, the Weizmann Institute, the Hebrew University of Jerusalem, the University of Potsdam, Texas Tech University, the University of California at Davis, the Danish Technical University and the Armagh Observatory and Planetarium. View this GCN Circular online at https://gcn.nasa.gov/circulars/40229. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38255] GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40228 SUBJECT: GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310 DATE: 25/04/24 09:42:20 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud Univ.), G. Corcoran (UCD), S. Covino (INAF/OAB), N. Habeeb (Leicester), L. Izzo (INAF/OACN and DARK/NBI), A. J. Levan (Radboud and Warwick), A. Martin-Carrillo (UCD), J. T. Palmerio (CEA/Irfu), G. Pugliese (API), B. Schneider (LAM), N. R. Tanvir (Leicester), S. D. Vergani (LUX-Paris Obs.), K. Wiersema (Hertfordshire), report on behalf of the Stargate collaboration: We observed the optical and NIR afterglow of GRB 250424A (Francile et al., GCN 40222; Cenko et al., GCN 40224; Brivio et al., GCN 40225; Becerra et al., GCN 40226) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Observations started on 2025 Apr 24.322 UT (0.87 hr after the Swift/BAT trigger) and consisted of a sequence of increasing exposure times (175, 300, 600, 1200, 1920 s). In the acquisition image (taken at a mid time of 0.851 hr after the Swift/BAT trigger), the counterpart is well detected with a magnitude r = 19.09 +- 0.02, calibrated against nearby stars from the SkyMapper catalog (Wolf et al. 2018, doi:10.4225/41/593620ad5b574). We detect a bright continuum over the wavelength range 3100 to 24,500 AA. Many absorption features are visible which we interpret as Mn II, Fe II, Mg II, Mg I, Ti II, Ca II, Na I, including a number of fine-structure transitions from Fe II*, all at a common redshift z = 0.310. At a consistent redshift, we also detect several emission lines, due to [O II], [O III], [S II], [N II], and the Balmer lines from the GRB host galaxy (Perez-Fournon et al., GCN 40227). We note that our redshift is consistent with the photometric determination z = 0.33 +/- 0.12 of the host redshift from the Legacy Survey (Zhou et al. 2021, doi:10.1093/mnras/staa3764). We acknowledge excellent support from the ESO observing staff in Paranal. View this GCN Circular online at https://gcn.nasa.gov/circulars/40228. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38254] GRB 250424A: likely host galaxy
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40227 SUBJECT: GRB 250424A: likely host galaxy DATE: 25/04/24 08:54:58 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), and A. López-Oramas (IAC and ULL) We report on the likely host galaxy of the Swift/BAT GRB 250424A (Cenko et al., GCN circ. 40224), with Swift/XRT and Swift/UVOT detections (Cenko et al., GCN circ. 40224) and detections in the optical by Global MASTER-net (Francile et al. GCN circ. 40222) and DDOTI (Becerra et al., GCN circ. 40226) and in the optical and near-IR by REM (Brivio et al., GCN circ. 40225). A catalogued Legacy Surveys DR10 (LS DR10) galaxy (RA, Dec = 217.4999, -35.0252) is visible at the position of the optical and near-IR counterpart of GRB 250424A, with magnitudes in the LS DR10 catalog of g=22.60, r=21.98, i=22.05, and z=21.70. This galaxy is located at about 0.3" from the Swift/UVOT position and 0.2" from the Global MASTER-net position. We propose that this galaxy is the host of GRB 250424A. View this GCN Circular online at https://gcn.nasa.gov/circulars/40227. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38253] GRB 250424A: DDOTI Afterglow Detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40226 SUBJECT: GRB 250424A: DDOTI Afterglow Detection DATE: 25/04/24 08:30:40 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Sahil Atri (U Roma), Alan M. Watson (UNAM), Eleonora Troja (U Roma), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM) and Margarita Pereyra (UNAM) report: We observed the field of the GRB 250424A detected by Swift/BAT (Cenko et al., GCN Circ. 40136) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2025-04-24 UTC from 07:23 UTC to 7:45 UTC (from T+30.6 h to T+53.5 min after the trigger) and obtained a total exposure of 20 minutes. Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we detect a source consistent with the UVOT position (Cenko et al., GCN Circ. 40136) and the previous optical detections (Francile et al., GCN Circ. 40222, Brivio et al., GCN Circ. 40225), with an AB magnitude of: w = 19.4 +/- 0.1 Further observations and analysis are ongoing. This value is not corrected for the Galactic extinction. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40226. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38252] GRB 250424A: REM optical/NIR afterglow detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40225 SUBJECT: GRB 250424A: REM optical/NIR afterglow detection DATE: 25/04/24 08:19:08 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio (INAF-OAB), A. Melandri (INAF-OAR), M. Ferro, P. D'Avanzo, S. Covino, G. Tagliaferri, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of GRB 250424A detected by Swift/BAT (Cenko et al., GCN 40224) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 April 24 at 06:54:31 UT (i.e. 123 s after the burst). From preliminary photometry, we detect the optical/NIR counterpart (Francile et al., 40222) at the Swift/UVOT position (Cenko et al., GCN 40224) with the following magnitudes: r = 17.7 +/- 0.1 (AB; calibrated against the SkyMappercatalogue), at a mid-time of 205 s after the trigger, H = 14.5 +/- 0.2 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 164 s after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/40225. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38251] GRB 250424A: Swift detection of a burst with an optical counterpart
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40224 SUBJECT: GRB 250424A: Swift detection of a burst with an optical counterpart DATE: 25/04/24 07:12:30 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> S. B. Cenko (GSFC), V. D'Elia (SSDC & INAF-OAR), J. J. DeLaunay (PSU), R. Gupta (NASA GSFC), A. Melandri (INAF-OAR), K. L. Page (U Leicester) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 06:52:28.51 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250424A (trigger=1306404). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 217.513, -35.022 which is RA(J2000) = 14h 30m 03s Dec(J2000) = -35d 01' 19" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single peak structure with a duration of about 30 sec. The peak count rate was ~25000 counts/sec (15-350 keV), at ~15 sec before the trigger. The XRT began observing the field at 06:56:39.3 UT, 250.9 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 217.50010, -35.02493 which is equivalent to: RA(J2000) = 14h 30m 00.03s Dec(J2000) = -35d 01' 29.7" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 39 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 does not constrain the column density. UVOT took a finding chart exposure of 150 seconds with the White filter starting 254 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 14:29:60.00 = 217.49998 DEC(J2000) = -35:01:30.6 = -35.02518 with a 90%-confidence error radius of about 0.63 arc sec. This position is 1 arc sec. from the center of the XRT error circle. The estimated magnitude is 18.80 with a 1-sigma error of about 0.15. No correction has been made for the expected extinction corresponding to E(B-V) of 0.064. Burst Advocate for this burst is S. B. Cenko (brad.cenko AT nasa.gov). 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/40224. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38250] Swift GRB250424.29: Global MASTER-Net observations report
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40223 SUBJECT: Swift GRB250424.29: Global MASTER-Net observations report DATE: 25/04/24 07:08:43 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB250424.29 (trigger No 1306404,14h 30m 03.12s , -35d 01m 19.2s, R=0.05) errorbox 94 sec after notice time and 178 sec after trigger time at 2025-04-24 06:55:26 UT, with upper limit up to 19.4 mag. The observations began at zenith distance = 25 deg. The sun altitude is -52.5 deg. The galactic latitude b = 23 deg., longitude l = 325 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2852168 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 198 | MASTER-OAFA | C | 40 | 19.4 | 244 | MASTER-OAFA | C | 40 | 19.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40223. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38249] Swift GRB250424.29: Global MASTER-Net OT detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40222 SUBJECT: Swift GRB250424.29: Global MASTER-Net OT detection DATE: 25/04/24 07:06:22 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina (Lomonosov MSU), O.Gress, N.Budnev(ISU), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the GRB250424.29 99 sec after notice time and 178 sec after trigger time at 2025-04-24 06:55:26 UT. On our first (40s exposure) set we found 1 optical transient within Swift error-box (ra=217.512 dec=-35.0214 r=0.05) brighter than 18.9. T-Tmid Date Time Expt. Ra Dec Mag ---------|---------------------|-------|-----------------|-----------------|------- 198 2025-04-24 06:55:26 40 (14h 29m 59.96s , -35d 01m 30.7s) 18.0 The 5-sigma upper limit has been about 18.9mag The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40222. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38248] LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40221 SUBJECT: LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates DATE: 25/04/24 05:12:11 GMT FROM: Haibin Zhang at National Astronomical Observatory of Japan (NAOJ) <haibin.zhang(a)nao.ac.jp> Haibin Zhang, Mitsuru Kokubo, Nozomu Tominaga, Yousuke Utsumi, Michitoshi Yoshida (NAOJ), Tomoki Morokuma (Chiba Tech), Akira Arai, Wanqui He, Yuki Moritani, Masato Onodera, Vera Maria Passegger, Ichi Tanaka, Kiyoto Yabe (NAOJ), Sean MacBride, Isaac McMahon, Marcelle Soares-Santos (UZH), Ken Herner (Fermilab), Simran Kaur (University of Michigan/UZH), Lillian Joseph (Benedictine U.), and Tom Diehl (FNAL) report on behalf of the Japanese Collaboration for Gravitational-Wave Electro-Magnetic Follow-up (J-GEM), Subaru Telescope, and Dark Energy Survey Gravitational Wave (DESGW) Team: Between 05:11 and 10:20 UTC on April 3, 2025, we carried out spectroscopic observations with the Subaru/Prime Focus Spectrograph (PFS) following the LVK alert issued for the gravitational-wave event S250328ae (GCN 39898). The Subaru/PFS is a fiber spectrograph capable of observing ~2400 targets simultaneously within a ~1.25 square degree field of view, and covers a wavelength range of 380 nm to 1260 nm with a resolving power of ~2500-5500 (Sugai et al. 2015; Tamura et al. 2024). We observed seven pointings centered on the ICRS coordinates listed below: |RA [deg]|Dec [deg]| | - | - | |144.130530|10.436230| |144.126501|11.595492| |145.151367|9.856599| |145.151367|11.015861| |145.151367|12.175123| |146.176234|11.595492| |146.180717|12.754753| These seven pointings cover the ~50% localization region of the S250328ae event. We observed targets selected from transient candidates of GCN 39934 and 39992 (including candidates before and after vetting), X-ray sources from GCN 39972, and potential host galaxies from GLADE+ (Dálya et al. 2022) and PS1-STRM (Beck et al. 2021) catalogs in our pointings. A total of ~3900 targets were observed with an on-source exposure time of 1800 seconds in six pointings and 900 seconds in one pointing (shortened due to bad weather conditions). We reduced the data on-site using the quick reduction system based on the PFS Data Reduction Pipeline, and then carried out classification (fitting galaxy, QSO, star, and supernova templates) and visual inspection. After classification and visual inspection, we obtained confident spectroscopic redshifts of ~70% of our targets. Among these sources, five candidates listed below were identified to be the possible electromagnetic counterpart to the gravitational-wave event S250328ae (within the ~90% three-dimensional localization volume partly covered by our pointings). Because these five candidates were originally selected from the GLADE+ and PS1-STRM catalogs that do not contain information of variability, we encourage follow-up observations to confirm their variability. |ID_PFS|ATNAME|RA [deg]|Dec [deg]|Type_PFS|Redshift| | - | - | - | - | - | - | |761|AT2019uib|145.718857|12.412288|QSO|0.130| |9238|N/A|145.412644|12.717089|QSO|0.096| |13647|N/A|144.989553|10.636089|QSO|0.136| |17165|N/A|145.733559|11.593362|QSO|0.120| |19826|N/A|145.351893|12.503455|QSO|0.136| No counterparts to X-ray sources (GCN 39972) are recovered within their reported error bounds by our observations. We do not identify any transient candidates (GCN 39934 and 39992) we observed within the ~90% three-dimensional localization volume of S250328ae. These transient candidates falling outside the ~90% localization volume are listed below. |ID_ DESGW|ATNAME|RA [deg]|Dec [deg]|Type_ DESGW|Type_PFS|Redshift| | - | - | - | - | - | - | - | |2290036|AT2025gek|145.199481|10.828527|SN_LIKE|SN Ic|0.233| |2290467|AT2020woa|144.388798|10.255536|SN_LIKE|SN Ib|0.050| |2292782|AT2025geo|144.928578|10.349243|SN_LIKE|SN Ia|0.182| |2290334|AT2025geq|145.235616|12.469694|SN_LIKE|SN Ia|0.186| |2290623|AT2025gen|144.112464|11.641817|AGN_LIKE|SN II|0.204| |2291223|N/A|146.389563|13.131801|AGN_LIKE|QSO|0.540| |2293190|AT2025cvb|144.191297|10.828462|SN_LIKE|SN Ia|0.140| |2290143|AT2025ggv|146.033906|11.088812|SN_LIKE|QSO|1.437| |2292040|AT2025ges|144.438216|9.885617|AGN_LIKE|SN Ia|0.434| |2290059|N/A|144.679961|10.018211|AGN_LIKE|QSO|0.209| |2292786|N/A|144.037664|10.810454|AGN_LIKE|SN Ia|0.254| |2293517|AT2025geu|145.956024|12.381673|AGN_LIKE|QSO|0.507| |2295862|N/A|145.361115|12.521385|AGN_LIKE|QSO|0.969| |2290563|N/A|145.149074|11.756403|AGN_LIKE|QSO|0.255| |2289995|AT2025ggx|144.57373|10.274445|SN_LIKE|SN II|0.358| We are grateful to the staffs at NAOJ and Subaru Telescope for their contributions to the deployments of PFS hardware and software, and the preparations of PFS system integration, engineering observations, and various other engineering works. Our thanks should also be propagated to the administrative staffs at Kavli IPMU, NAOJ, Subaru Telescope, and all the PFS institutes for kind supports in such aspects as finances, contracts, asset managements, and so on. This research is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has the cultural, historical, and natural significance in Hawaii. The DECam Search & Discovery Program for Optical Signatures of Gravitational Wave Events (DESGW) is carried out by the Dark Energy Survey (DES) collaboration in partnership with wide-ranging groups in the community. DESGW uses data obtained with the Dark Energy Camera (DECam), which was constructed by the DES collaboration with support from the Department of Energy and member institutions, and utilizes data as distributed by the Science Data Archive at NOIRLAB. NOIRLAB is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. We thank the Cerro Tololo observatory staff for their support in acquiring these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40221. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38247] EP250421a: Nickel optical upper limit
by GCN Circulars 23 Apr '25

23 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40220 SUBJECT: EP250421a: Nickel optical upper limit DATE: 25/04/23 23:13:36 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> Katherine Mora, Eyouel Abate, Ansel Parke, WeiKang Zheng and Alex Filippenko (UC Berkeley) report on behalf of the KAIT GRB team: We observed the field of EP250421a (Zhao et al., GCN 40198) with the 1-m Nickel telescope located at Lick observatory, California. Observations were performed in the R band with 600s x 6 exposures. In our coadd image, we do not detect the optical afterglow (Lee et al., GCN. 40192; Fu et al., GCN 40193; Liu et al., GCN 40197), with an upper limit of R > 20.5 (Vega) at a mid-time of 14.9 hours after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/40220. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38246] EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963
by GCN Circulars 23 Apr '25

23 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40219 SUBJECT: EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963 DATE: 25/04/23 18:19:28 GMT FROM: Jonathan Quirola at Radboud University <jaquirola1990(a)gmail.com> Andrew J. Levan (Radboud), Jonathan Quirola-Vásquez (Radboud), Peter G. Jonker (Radboud), Franz E. Bauer (UTA), Antonio Martin-Carrillo (UCD), Daniele B. Malesani (DAWN/ NBI and Radboud), Javi Sánchez-Sierras (Radboud), Maria E. Ravasio (Radboud), Agnes van Hoof (Radboud), Jennifer Chacon (PUC), Joyce van Dalen (Radboud), Gregory Corcoran (UCD) report on behalf of a larger collaboration: We observed the optical and X-ray counterpart (Levan et al., GCN 40160; Sbarrato et al., GCN 40166) of the Einstein Probe (EP) transient EP250416a (Zhao et al., GCN 40154, 40165), also identified as GRB 250416C (Svinkin et al., GCN 40167; Wang et al., GCN 40184). Observations were carried out using the Gemini South telescope located on Cerro Pachon, Chile, equipped with the GMOS-S instrument in spectroscopy mode. Observations started on 2025-04-17 at 07:44:43 (i.e., ~0.58 days after the EP detection), and consisted of 4 exposures of 900 s each using the B480 grating, covering the wavelength range between ~4000 and 9500 AA. In our spectrum, we clearly detect an emission line at 7317 AA. Considering the most likely options for this feature (Halpha, Hbeta, [O III], [O II]), the interpretation more consistent with the data is the (unresolved) [O II] 3727/3729 doublet at z = 0.963. In all other cases, we would expect to see other features which would fall over well-covered regions of the spectrum, which are not observed. We thus suggest that this is the redshift of the host galaxy of EP250416a. The spectrum shows tentative absorption features at the expected locations of Mg II (2796, 2803 AA) and Mg I (2852 AA) at z = 0.962, although the signal to noise in the blue region of the spectrum is badly affected by the bright Moon, hence we cannot conclusively determine an absorption redshift. We acknowledge excellent support from the Gemini South staff. View this GCN Circular online at https://gcn.nasa.gov/circulars/40219. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38245] EP250421a: Upper limits from Fermi-GBM Observations
by GCN Circulars 23 Apr '25

23 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40218 SUBJECT: EP250421a: Upper limits from Fermi-GBM Observations DATE: 25/04/23 14:26:25 GMT FROM: mariaedvige.ravasio(a)ru.nl M. E. Ravasio (Radboud Univ.), E. Burns (LSU), C. Malacaria (INAF-OAR) and P.G. Jonker (Radboud Univ.) report on behalf of the Fermi-GBM Team: Fermi-GBM had full spatial coverage of the transient EP250421a detected by EP-WXT (Zhao et al., GCN 40198). There was no Fermi-GBM onboard trigger around the EP starting time T0=2025-04-21T16:16:28 UTC. The GBM targeted search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [T0-50;T0+500] s, seeking signals between 64 ms and 32.768 s in duration. A candidate was found at T0+380 s, but its location is not consistent with the EP transient. No signal consistent with the EP transient, both temporally and spatially, is identified, as confirmed also by visual inspection of the data. Assuming a “soft” spectral template (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7), and a duration of 8.192 s, we derive a flux upper limit of 3.7e-08 erg/cm2/s in the energy band 10-1000 keV. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/40218. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38244] SVOM/sb25042207: XRT observations
by GCN Circulars 23 Apr '25

23 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40217 SUBJECT: SVOM/sb25042207: XRT observations DATE: 25/04/23 13:45:35 GMT FROM: Antonino D'Ai' at IASF-PA <antonino.dai(a)inaf.it> Antonino D'Aì (INAF/IASFPA), J. A. Kennea (PSU), Elena Ambrosi (INAF/IASFPA), Valerio D'Elia (SSDC & INAF-OAR), Andrea Melandri (INAF-OAR) reports on behalf of the Swift-XRT team: We have analysed 1.8 ks of XRT data for the SVOM/ECLAIRs-detected X-ray transient sb25042207 (Liang et al., GCN Circ. 40213), from T0+3.8 ks to T0+5.6 ks after the SVOM/ECLAIRs trigger. The data are entirely in Photon Counting (PC) mode. We detect two previously known X-ray sources and two uncatalogued X-ray sources within the ECLAIRs error circle. We note that the ECLAIRs error region overlaps with the Coma cluster region, a well-known galaxy cluster that exhibits significant diffuse X-ray emission. Details of the uncatalogued sources: Source 2: RA (J2000): 194.93972 = 12:59:45.53 Dec (J2000): +27.8781 = +27:52:41.0 Error: 6.0 arcsec (radius, 90% confidence) Count rate: 8 (+5, -4) x 10^-3 ct/s Flux: [3.5 (+2.1, -1.9)] x 10^-13 erg/cm^2/s (observed, 0.3–10 keV) Source 4: RA (J2000): 195.13942 = 13:00:33.46 Dec (J2000): +27.7478 = +27:44:52.0 Error: 7.5 arcsec (radius, 90% confidence) Count rate: 0.011 (+0.005, -0.004) ct/s Flux: [4.8 (+2.1, -1.8)] x 10^-13 erg/cm^2/s (observed, 0.3–10 keV) Both sources are below the RASS limit and show no definitive signs of fading. The results of the XRT team's automatic analysis of the tiled XRT observations, including a position-specific upper limit calculator, are available at: https://www.swift.ac.uk/SVOM/SVOM_FIELD00013/ This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40217. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38243] SVOM/sb25042207: BOOTES-2 early optical upper limit
by GCN Circulars 23 Apr '25

23 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40216 SUBJECT: SVOM/sb25042207: BOOTES-2 early optical upper limit DATE: 25/04/23 07:34:37 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> M. Gritsevich (Univ. of Helsinki), I. Perez-Garcia, M.D. Caballero-Garcia, E. J. Fernandez-Garcia, R. Sanchez-Ramirez, S.-Y. Wu, S. Guziy, and A. J. Castro-Tirado (IAA-CSIC, Granada), Y.-D. Hu (GXU), C. Perez del Pulgar and A. Reina (Univ. of Malaga), R. Fernandez-Munoz (IHSM/UMA-CSIC), and M. Jelinek (ASU-CAS, Ondrejov Obs.), on behalf of a larger collaboration, report: Following the detection of the X-ray transient sb25042207 by SVOM (Liang et al. GCNC [40213](https://gcn.nasa.gov/circulars/40213)), the 0.6m BOOTES-2/TELMA robotic telescope at IHSM UMA “La Mayora” (Malaga, Spain) automatically responded to this high-energy event starting on Apr 22, 23:38:10 UT (i.e. 2 min after alert). On a coadd (20) of images at 00:00:50 UT (mid exposure time; i.e. 24 min post detection), nothing is detected down to 18.1 mag (clear filter), in agreement with the deeper observations taken later on (Belkin et al., GCNC [40215](https://gcn.nasa.gov/circulars/40215)). We would like to thank the staff at IHSM-/UMA-CSIC “La Mayora” for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/40216. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38242] SVOM/sb25042207: GOTO optical upper limits
by GCN Circulars 23 Apr '25

23 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40215 SUBJECT: SVOM/sb25042207: GOTO optical upper limits DATE: 25/04/23 06:57:54 GMT FROM: Sergey Belkin at Monash University <sergey.belkin(a)monash.edu> S. Belkin, A. Kumar, G. Ramsay, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, 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 optical observations with the Gravitational-wave Optical Transient Observer (GOTO, Steeghs et al. 2022; Dyer et al. 2024) in response to the SVOM/ECLAIRs alert sb25042207 (Liang et al., GCN 40213). Targeted observations were performed on April 22 2025 23:39:55 UT (+1.06 h post trigger) and on April 23 2025 01:20:48 UT (+2.74 h post trigger). The first epoch of observations consisted of 4x90 s exposures, while the second epoch was obtained in survey mode with 4x45 s exposures. All images were taken 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. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks. No new transients that could be credibly associated with SVOM/ECLAIRs sb25042207 were detected down to a 5-sigma L-band limiting magnitude of 20.4. Additionally, no source is detected prior to the GRB trigger time in archival GOTO observations (4x45 s; in survey mode) taken 1.347 h before the trigger, down to a 5-sigma L-band upper limit of 19.7 mag. 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 and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/40215. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38241] GRB 250421A: AstroSat CZTI detection
by GCN Circulars 23 Apr '25

23 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40214 SUBJECT: GRB 250421A: AstroSat CZTI detection DATE: 25/04/23 06:55:12 GMT FROM: Varun Bhalerao at IIT Bombay <varunb(a)iitb.ac.in> M. Tembhurnikar (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long-duration GRB 250421A which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 40191) and Konus-Wind (IPN Notices). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-04-21 10:38:34.50 UTC. The measured peak count rate associated with the burst is 137 (+34, -32) counts/s above the background in the combined data of three quadrants (out of four), with a total of 294 (+129, -105) counts. The local mean background count rate was 230 (+3, -5) counts/s. Using cumulative rates, we measure a T90 of 5.6 (+1.7, -3.3) s. The source was also faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-04-21 10:38:34.17 UTC. The measured peak count rate associated with the burst is 261 (+67, -71) counts/s above the background in the combined data of all quadrants, with a total of 623 (+290, -324) counts. The local mean background count rate was 1349 (+10, -10) counts/s. We measure a T90 of 4.8 (+1.3, -3.1) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/40214. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38240] SVOM/sb25042207: SVOM detection of an X-ray transient
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40213 SUBJECT: SVOM/sb25042207: SVOM detection of an X-ray transient DATE: 25/04/22 23:53:42 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Yifang Liang (PMO), Ziqi Wang (GXU), Wenjin Xie (NAOC), Stephane Schanne (CEA) report on behalf of the SVOM mission team: SVOM/ECLAIRs triggered on the X-ray transient labelled sb25042207 (SVOM burst-id sb25042207) starting at 2025-04-22T22:36:17 UTC (Tb). 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 Image Trigger (IMT), which produced a sequence of 1 alert. IMT provided the alert with the best signal-to-noise ratio (SNR) of 7.01 in the 5-8 keV energy band over a time window of 1310.72 seconds starting at Tb. The localization of the best alert is R.A., Dec 194.9273, 27.7745 degrees: RA (J2000) = 12h59m42.56s Dec (J2000) = 27d46m28.13s with a 90% C.L. radius of 11.17 arcmin (including systematic error of 2 arcmin added in quadrature). We notice the presence of many X-ray candidate sources inside the error region, including 2 QSOs, as well as 2 nearby AGNs including Mrk 60. SVOM did not slew to this transient because it did not exceed the slew threshold. SVOM follow-up observations will be scheduled. 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. The Burst Advocate (BA) on shift for this transient is Yifang Liang: yfliang(a)pmo.ac.cn Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/40213. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38239] GRB250419A: VLA radio detection
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40212 SUBJECT: GRB250419A: VLA radio detection DATE: 25/04/22 21:29:01 GMT FROM: Genevieve Schroeder at Cornell University <genevieveschroeder(a)u.northwestern.edu> Genevieve Schroeder (Cornell), Anna Ho (Cornell), Daniel Perley (LJMU) report: We observed the position of the SVOM/ECLAIRs GRB 250419A (Wang et al. GCN 40168), with the NSF’s Karl G. Jansky Very Large Array (VLA) under program 25A-374 (PI Perley) beginning on 2025 April 22 at 06:37 UT (3.2 days post discovery) at a mean frequency of 10 GHz (4 GHz bandwidth). Based on preliminary analysis, we clearly detect a radio source with a 10 GHz flux density of ~320 uJy and a position of: RA(J2000) = 13:29:37.275 Dec(J2000) = +07:02:27.63 with an uncertainty of ~0.2" in each coordinate. This is consistent with the location of the optical counterpart of GRB 250419A (López et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172; Thakur et al., GCN 40174; Lipunov et al., GCN 40179; Odeh et al., GCN 40180; Perley & Bochenek, GCN 40181; Pankov et al., GCN 40182; Pérez-Fournon et al., GCN 40183; Kuin, GCN 40185; Wu et al., GCN 40186; Xie et al., GCN 40187; Jiang et al., GCN 40188; Ghosh et al., GCN 40189; Bochenek & Perley, GCN 40190; Pankov et al., GCN 40202; Gianluca Masi, GCN 40206; Giovanni Calapai & Massa S. Giorgio, GCN 40209; Lagioia et al., GCN 40210). At the redshift of GRB 250419A (Thakur et al., GCN 40174), the VLA observation corresponds to a 18.5 GHz (rest-frame) luminosity of ~1e31 erg/s/Hz. This luminosity is similar to a typical long GRB radio afterglow at a similar epoch (e.g., Chandra & Frail 2012, ApJ 746, 156, Laskar et al. 2023, ApJ, 946, 23). Additional followup is planned. We thank the VLA staff for quickly approving and executing these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40212. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38238] IceCube-250421A: DDOTI Detection of the LAST Candidate
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40211 SUBJECT: IceCube-250421A: DDOTI Detection of the LAST Candidate DATE: 25/04/22 19:03:39 GMT FROM: sahil.atri(a)students.uniroma2.eu Sahil Atri (U Roma), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Eleonora Troja (U Roma), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM) and Margarita Pereyra (UNAM) report: We observe the field of the IceCube-250421A (bronze) event with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on the Sierra of San Pedro Martir (http://ddoti.astroscu.unam.mx) on the night of 2025-04-22 UTC. DDOTI automatically pointed to the region centred in RA, Dec (J2000)= 16:03:46.49 +28:43:50.8, covering about 96% of the IceCube error region. DDOTI observed from 04:50 UTC to 11:47 UTC (from T+ 11.74 h to T+ 18.69 h after the trigger) with a total exposure of 3.5 hours, alternating with other scientific programs. Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues, we detect the candidate reported by SN 2025cbj at w=18.53+/0.04, consistent with the observations from the Large Array Survey Telescope (Garrappa et al., GCN Circ. 40208). No other uncatalogued sources within the observed field to an average 10-sigma limiting AB magnitude of: w > 20.7 This value is not corrected for the Galactic extinction. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40211. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38237] IceCube-250421A: DDOTI Detection of the LAST Candidate
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40211 SUBJECT: IceCube-250421A: DDOTI Detection of the LAST Candidate DATE: 25/04/22 19:03:39 GMT FROM: sahil.atri(a)students.uniroma2.eu Sahil Atri (U Roma), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Eleonora Troja (U Roma), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM) and Margarita Pereyra (UNAM) report: We observe the field of the IceCube-250421A (bronze) event with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on the Sierra of San Pedro Martir (http://ddoti.astroscu.unam.mx) on the night of 2025-04-22 UTC. DDOTI automatically pointed to the region centred in RA, Dec (J2000)= 16:03:46.49 +28:43:50.8, covering about 96% of the IceCube error region. DDOTI observed from 04:50 UTC to 11:47 UTC (from T+ 11.74 h to T+ 18.69 h after the trigger) with a total exposure of 3.5 hours, alternating with other scientific programs. Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues, we detect the candidate reported by SN 2025cbj at w=18.53+/0.04, consistent with the observations from the Large Array Survey Telescope (Garrappa et al., GCN Circ. 40208). No other uncatalogued sources within the observed field to an average 10-sigma limiting AB magnitude of: w > 20.7 This value is not corrected for the Galactic extinction. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40211. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38236] GRB 250419A: Mephisto Multi-band Optical Detection
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40210 SUBJECT: GRB 250419A: Mephisto Multi-band Optical Detection DATE: 25/04/22 17:40:55 GMT FROM: Chenxu Liu at Mephisto Team <cxliu(a)ynu.edu.cn> Edoardo Lagioia, Chenxu Liu, Yuan Fang, Guowang Du, Donglin Gao, Zhang Zepeng, Jinghua Zhang, Brajesh Kumar, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team: We conducted simultaneous multi-band photometric observations of the gamma-ray burst GRB 250419A (SVOM/ECLAIRs trigger sb25041901 at 2025-04-19T02:29:32 UTC; Wang et al. GCN 40168) with the Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University, located at the Lijiang Observatory. The observations extend over two nights from 19 to 20 April 2025. An optical counterpart is detected in the u-, g-, r-, i-band stacked images but not in the v-, z-band stack. The preliminary photometry and the 3σ upper limits are listed below. UT start |T-T0 (hr)| Band | Exp | Mag/LimMag (AB) -------------------|---------|------|--------|-------------------------- 2025/4/19 21:13:29 | 18.73 | u | 2x300s | > 20.63 2025/4/19 21:25:42 | 18.94 | v | 2x300s | > 20.91 2025/4/19 21:13:29 | 18.73 | g | 2x300s | 19.84 +/- 0.19 2025/4/19 21:25:42 | 18.94 | r | 2x300s | 19.92 +/- 0.10 2025/4/19 21:13:29 | 18.73 | i | 2x300s | 19.58 +/- 0.12 2025/4/19 21:25:42 | 18.94 | z | 2x300s | > 20.27 * Note: The above two sets of 300s exposures are taken at altitude ~ 23 deg. UT start |T-T0 (hr)| Band | Exp | Mag/LimMag (AB) -------------------|---------|------|--------|-------------------------- 2025/4/20 17:10:04 | 38.68 | u | 2x300s | 21.47 +/- 0.39 2025/4/20 17:10:06 | 38.68 | g | 2x300s | 21.00 +/- 0.17 2025/4/20 17:10:04 | 38.68 | i | 2x300s | 20.42 +/- 0.18 -------------------|---------|------|--------|-------------------------- 2025/4/20 19:50:05 | 41.34 | v | 1x300s | > 22.18 2025/4/20 19:50:04 | 41.34 | r | 1x300s | 21.15 +/- 0.29 2025/4/20 19:50:07 | 41.34 | z | 1x300s | > 21.30 Follow-up observations have already confirmed the presence of an optical counterpart ((López et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172; Thakur et al., GCN 40174; Lipunov et al., GCN 40179; Odeh et al., GCN 40180; Perley & Bochenek, GCN 40181; Pankov et al., GCN 40182; Pérez-Fournon et al., GCN 40183; Kuin, GCN 40185; Wu et al., GCN 40186; Xie et al., GCN 40187; Jiang et al., GCN 40188; Ghosh et al., GCN 40189; Bochenek & Perley, GCN 40190; Pankov et al., GCN 40202; Gianluca Masi, GCN 40206; Giovanni Calapai & Massa S. Giorgio, GCN 40209). The ESO/X-Shooter spectroscopic observations identify a redshift of z = 0.845 (Thakur et al., GCN 40174). ---------------------------------------------------------- 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. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21. ---------------------------------------------------------- View this GCN Circular online at https://gcn.nasa.gov/circulars/40210. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38235] GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40209 SUBJECT: GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations. DATE: 25/04/22 15:45:12 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 250419A detected by SVOM/ECLAIRs (Wang et al. GCN 40168) with the 11 inches Schmidt-Cassegrain (Celestron 11) telescope F/D=6,3. The observations were started at 2025-04-19 23:55 UT (approximately 21.43 hours after burst) stacking a set of unfiltered CCD image. The observations were carried out with clear skies and good visibility conditions. The OT was detected at the following position: RA (J2000.0) 13h 29m 37.33s Decl. (J2000.0) +07° 02' 27.5" Photometry was obtained using nearby PanSTARRS stars as follows: Observation Mid-Time T-T0 (hr) Exposure Filter Mag. Err. 2025-04-20 01:19:29 UT 22.83 164x60s CR 19.76 +/-0.06 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 López et al. (GCN 40169), Xin et al. (GCN 40170), Zheng et al. (GCN 40171), Kumar et al. (GCN 40172), Lipunov et al. (GCN 40179), Odeh et al. (GCN 40180), Perley & Bochenek (GCN 40181), Pankov et al. (GCN 40182), Pérez-Fournon et al. (GCN 40183), Kuin (GCN 40185), Wu et al. (GCN 40186), Xie et al. (GCN 40187), Jiang et al. (GCN 40188), Ghosh et al. (GCN 40189), Bochenek & Perley (GCN 40190), Pankov et al. (GCN 40202), Masi (GCN 40206). The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40209. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38234] IC-250421A: LAST optical observations of the IceCube neutrino candidate
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40208 SUBJECT: IC-250421A: LAST optical observations of the IceCube neutrino candidate DATE: 25/04/22 13:56:21 GMT FROM: Simone Garrappa at Weizmann Institute of Science <simone.garrappa(a)weizmann.ac.il> S. Garrappa (WIS), R. Konno (WIS), E. A. Zimmerman (WIS), A. Horowicz (WIS), E. O. Ofek (WIS), S. Ben-Ami (WIS), D. Polishook (WIS), O. Yaron (WIS), S. Fainer (WIS), P. Chen (WIS), A. Krassilchtchikov (WIS), Y. M. Shani (WIS), E. Segre (WIS), A. Gal-Yam (WIS), S. Spitzer (WIS), and K. Rybicki (WIS) on behalf of the LAST Collaboration. We report the observations of the IceCube Bronze neutrino candidate IC-250421A with the Large Array Survey Telescope (LAST, Ofek et al. 2023; Ben-Ami et al. 2023). We observe the field of IC-250421A using four telescopes, each with a FoV of 7.4 deg^2 and no filter (clear - similar to the GAIA Bp band) over several epochs. In each epoch, we coadd 20x20s images. We observed for a total of 19 epochs under bright moon conditions, with an average limiting magnitude of 19.70 (AB). We find one candidate transient optical counterpart in our automatic transient-detection pipeline (Konno et al., in prep.). This is SN2025cbj, a known SN candidate classified as Type IIn (Sollerman et al., 2025) at redshift z = 0.07, which was discovered by ZTF on 20 02 2025 (~60 days before T0, https://alerce.online/object/ZTF25aagbrpb). SN2025cbj is located at ~1.8 deg distance from the IceCube best-fit localization, within the 90% localization error. We began observations on 21 04 2025 at 22:19:54 UTC (T-T0 = 5.23 hours). The observations cover part of the 90% neutrino footprint reported in GCN#40195 with predefined LAST observation fields. The following LAST field was observed: | Field| RA | Dec | Time | Limiting Mag (AB) | | ---- | ------ |-------- |----------- |------------ | | 1294 | 242.22 | 27 | 2459326.43 | 19.70 | Here we report the average brightness during the night: | RA (J2000)|Dec (J2000)| Mag (AB) | MagErr | Comment | | ---------- |-----------|-----------|--------|-------------| | 239.916993 | 27.111324 | 18.53 | 0.07 | SN 2025cbj | On 04 04 2025 (~17 days before T0) LAST observed the same field during nominal all-sky survey operations and detected SN2025cbj. We report the average source brightness from these archival observations. | RA (J2000)|Dec (J2000)| Mag (AB) | MagErr | Comment | | ---------- |-----------|-----------|--------|-------------| | 239.916993 | 27.111324 | 18.52 | 0.06 | SN 2025cbj | The reported magnitudes are in the AB system, calibrated using the LAST absolute photometric calibration pipeline (Garrappa et al. 2024). All reported errors are statistical only. The monitoring of this field will continue during LAST sky survey operations. We encourage multi-wavelength follow-up observations of this source. LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/). View this GCN Circular online at https://gcn.nasa.gov/circulars/40208. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38233] EP250421a: NOT optical observations
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40207 SUBJECT: EP250421a: NOT optical observations DATE: 25/04/22 13:46:09 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> D. B. Malesani (DAWN/NBI and Radboud), J. Sanchez-Sierras (Radboud), A. Martin-Carrillo (UCD), J. Quirola-Vásquez (Radboud), P. G. Jonker (Radboud), A. J. Levan (Radboud and Warwick), D. Xu (NAOC), Z. P. Zhu (NAOC), H. Dawson (IAP Potsdam), report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP250421a (Zhao et al., GCN 40198) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were carried out under poor seeing (1.8") in the r and z filters (3x300 s, each) starting on 2025-04-21 at 22:04:12 UT (5.79 hr after the trigger). At the location of the optical counterpart reported by Lee et al. (GCN 40192), Fu et al. (GCN 40193), and Liu et al. (GCN 40197), also consistent with the EP/FXT and Swift/XRT positions (Zhao et al., GCN 40198; Salvaggio et al., GCN 40204), we only marginally detect a source with r = 23.8 +/- 0.3 (AB), calibrated against nearby Pan-STARRS objects. View this GCN Circular online at https://gcn.nasa.gov/circulars/40207. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38232] GRB 250419A: Optical Observations via Virtual Telescope Project
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40206 SUBJECT: GRB 250419A: Optical Observations via Virtual Telescope Project DATE: 25/04/22 13:17:41 GMT FROM: Gianluca Masi at Virtual Telescope Project <gianluca(a)bellatrixobservatory.org> Gianluca Masi, Virtual Telescope Project (Italy), reports: We observed the field of GRB 250419A (Wang et al., GCN 40168) with the 14” robotic unit available at the Virtual Telescope Project facility in Manciano, Italy, equipped with a KAF-3200E based CCD camera. We collected 3, 300-second unfiltered exposures, then we averaged them. The central time of the resulting stack was 19 April, 21:07 UTC, that is about 18.6 hours after the burst. We clearly detect the optical counterpart of GRB 250419A. The position of the source is RA: 13 29 37.26; Decl.: +07 02 28.0 (J2000.0, mean residuals of 0.05”, reference stars from GaiaDR2) and the magnitude was estimated to be 19.3 (SNR=12, assuming R mags for the reference stars from GaiaDR2). The image is available here: https://www.virtualtelescope.eu/2025/04/22/grb-250419a-detection-of-the-opt… View this GCN Circular online at https://gcn.nasa.gov/circulars/40206. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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