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[vsnet-grb-info 42189] EP260321a: Einstein Probe detection of an X-ray transient
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44068 SUBJECT: EP260321a: Einstein Probe detection of an X-ray transient DATE: 26/03/21 13:01:43 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q.J. Huang (PMO, CAS), Z. C. Zou (NJU), X. Mao, D. Y. Li, H. W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260321a. The transient triggered EP-WXT (ID: 01709259023) at 2026-03-21T12:30:18 (UTC). The WXT position of the source is R.A. = 149.894 deg, DEC = 0.397 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 149.9260 deg, DEC = 0.4181 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. 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/44068. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42188] GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44067 SUBJECT: GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations DATE: 26/03/21 11:45:32 GMT FROM: A. Brosio at ABObservatory Rosarno <antonino.brosio(a)gmail.com> A. Brosio (ABObservatory Rosarno), M. A. Tripodi (ABObservatory Rosarno), S. Savaglio (Università della Calabria), S. Benatti (INAF - Osservatorio Astronomico di Palermo), M. Basilicata, M. Rainer (INAF - Osservatorio Astronomico di Brera), S. Tosi (Università di Genova), A. Di Dato (INAF - Osservatorio Astronomico di Capodimonte), D. Liguori (Osservatorio "G. Galilei", Liceo Scientifico Cariati), A. Nastasi (GAL Hassin, Isnello), E. Pace, R. Stanga, L. Betti (Università di Firenze - Osservatorio Polifunzionale del Chianti), D. Ricci (INAF - Osservatorio Astronomico di Padova) and the NOCTIS Collaboration report: We observed the optical counterpart of GRB 260310A / AT 2026FGK, previously reported by several groups as the optical afterglow: (O'Neill et al. 2026, TNS Discovery Report 294132; Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979; Méndez et al., GCN 43980; de Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Pursiainen et al., GCN 43990; Becerra et al., GCN 43991; Li et al., GCN 43993; Jayaraman et al., GCN 43994; Stein et al., GCN 43996; Martin-Carrillo et al., GCN 44000; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo et al., GCN 44003; Brivio et al., GCN 44004; Moskvitin et al., GCN 44006; Romanov, GCN 44020; Pawar et al., GCN 44022; Belkin et al., GCN 44043; Li et al., GCN 44044; Gupta et al., GCN 44051; Salunke et al., GCN 43958; Becerra et al., GCN 44059; Volnova et al., GCN 44060; Busmann et al., GCN 44061). At JD 2461120.34019 (2026-03-20.84019 UT), we measured the source at: AT 2026FGK 18.92 +/- 0.10 Sloan r Photometric calibration was performed using the APASS catalog, adopting the comparison stars at coordinates RA(J2000) = 219.274765, Dec(J2000) = +71.914946; RA(J2000) = 219.311345, Dec(J2000) = +71.880330. View this GCN Circular online at https://gcn.nasa.gov/circulars/44067. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42187] GRB 260318A: Glowbug gamma-ray detection
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44066 SUBJECT: GRB 260318A: Glowbug gamma-ray detection DATE: 26/03/21 11:28:43 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260318A, which was also detected by Fermi/GBM (GCN 44049), GECAM-B (GCN 44052), and SVOM/GRM (GCN 44055). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-03-18 22:35:52.696 with a duration of 7.7 s and a total significance of about 18.1 sigma. The light curve comprises two peaks at ~T0+2s and ~T0+6s. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44066. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42186] GRB 260310A / AT 2026fgk: KAIT optical observations
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44065 SUBJECT: GRB 260310A / AT 2026fgk: KAIT optical observations DATE: 26/03/21 06:49:53 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, observed the field of GRB 251022A (Fermi GBM Team, GCN 43951; Salunke et al., GCN 43958) on March 13, 14, 18 19, 20 UT. A set of B, V, R, I and clear (roughly R) filter images were obtained. We clearly detected the optical afterglow (O'Neill et al. 2026, TNS Discovery Report 294132; Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978;Martin-Carrillo et al., GCN 43979; Méndez et al., GCN 43980;de Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Pursiainen et al., GCN 43990; Becerra et al., GCN 43991; Li et al., GCN 43993; Jayaraman et al., GCN 43994; Stein et al., GCN 43996;Martin-Carrillo et al., GCN 44000; Moreno Méndez et al., GCN 43980; Becerra et al., GCN 43991; Li et al., GCN 43993; Stein et al., GCN 43996; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo et al., GCN 44003; Brivio et al., GCN 44004; Moskvitin et al., GCN 44006; Romanov, GCN 44020; Brosio et al., GCN 44021; Pawar et al., GCN 44022; Belkin et al., GCN 44043; Li et al., GCN 44044; Gupta et al., GCN 44051; Salunke et al., GCN 43958; Becerra et al., GCN 44059; Volnova et al., GCN 44060; Busmann et al., GCN 44061) in our coadd images and photometry in R band gives the following result: t-t0(d) Mag err ------------------ 3.21 17.98 0.03 4.25 18.31 0.02 8.24 18.34 0.02 9.22 18.30 0.02 10.20 18.54 0.03 View this GCN Circular online at https://gcn.nasa.gov/circulars/44065. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42185] GRB 260320A: NuSTAR detection of prompt emission
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44064 SUBJECT: GRB 260320A: NuSTAR detection of prompt emission DATE: 26/03/21 04:53:08 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 260320A in both the NuSTAR CsI anti-coincidence shields. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm, triggered at 2026-03-20 19:40:03.9 UTC, shows a detection of GRB 260320A consistent with SVOM/GRM (GCN Notices). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a single bright peak lasting for ~10-s. The peak count rate is ~2000-cps with a baseline rate of ~1000-cps during this time period. We do not see any evidence in the signal above 100 keV in the CdZnTe detectors. The SVOM/GRM localization (GCN Notices) at RA = 38.93, Dec = 16.64 implies an offset from the NuSTAR boresight of 92-deg (i.e. from the side of the instrument) and an offset from the geocenter of 14-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260320A Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/44064. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42184] GRB 260310A / AT2026fgk: NuSTAR follow-up detection
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44063 SUBJECT: GRB 260310A / AT2026fgk: NuSTAR follow-up detection DATE: 26/03/21 04:50:06 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> Elias Kammoun (Caltech), Gaurav Waratkar (Caltech), Rahul Jayaraman (Cornell), K-Ryan Hinds (Caltech), Anna Y. Q. Ho (Cornell) report: In response to our NuSTAR DDT request (PI Waratkar), NuSTAR observed the position of GRB 260310A / AT2026fgk (Fermi GBM team, GCN 43951; Arya et al., GCN 43958; Konno et al., GCN 43974; Martin-Carrillo et al., GCN 43979, 44000; Méndez et al., GCN 43980; Becerra et al., GCN 43991; Jayaraman et al., GCN 43994; Stein et al., GCN 43996; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo et al., GCN 44003; Brivio et al., GCN 44004; Rhodes et al., GCN 44005; Moskvitin et al., GCN 44006; Romanov et al., GCN 44020; Brosio et al., GCN 44021; Pawar et al., GCN 44022; Belkin et al., GCN 44043; Li et al., GCN 44044; Giarratana et al., GCN 44045; Gupta et al., GCN 44051; Ho et al., GCN 44057; Passaleva et al., GCN 44058; Becerra et al., GCN 44059; Volnova et al., GCN 44060), beginning at 2026-03-20T17:20:02 UTC with an exposure time of 7523 s. We performed a preliminary analysis of the NuSTAR spectrum in the 3-79 keV energy range from both the FPMA and FPMB modules by fitting an absorbed power law. We find a photon index of 1.76 ± 0.22 with an unabsorbed flux of (1.16 ± 0.15) x 10^-12 ergs/cm2/s (2-10 keV). All the uncertainties are 90% CL. At the reported redshift of 0.153 (Ugarte Postigo et al., GCN 43984; Hinds et al., GCN 43977), this would correspond to a luminosity (2-10 keV) of (7.2 ± 0.7) x 10^43 erg/s. We thank the entire NuSTAR Science & Mission operations teams for the rapid approval and execution of this DDT observation. NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/44063. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42183] EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44062 SUBJECT: EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare DATE: 26/03/21 03:19:15 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, automatically responded to the EP-WXT trigger 01709258989 (Zhou et al. GCN 44054) starting at 04:57 UT, about 2.4 hours after the trigger. A set of clear (roughly R) filter images were obtained and lasted for ~2.5 hours. Photometry on the suggested flare star 1RXS J073101.9+460030 (confirmed by Perez-Garcia et al., GCN 44056) show that its brightness remain around 12.5 mag for about 1 hour, then another flare started at 06:05 UT (3.53 hours after trigger), brightened to ~12.0 mag at peak time of 06:11 UT, then decreased to ~12.4 mag around 06:23 UT. This confirming the EP X-ray trigger is related to the stellar flare. View this GCN Circular online at https://gcn.nasa.gov/circulars/44062. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42182] GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44061 SUBJECT: GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening DATE: 26/03/21 01:42:34 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann, Daniel Gruen (LMU), Xander J. Hall, Brendan O'Connor, Antonella Palmese (CMU) report: We observed the optical/NIR counterpart of GRB 260310A (Fermi GBM team, GCN 43951; Salunke et al., GCN 43958), AT 2026fgk (e.g. O'Neill et al. 2026, TNS Discovery Report 294132; Konno et al., GCN 43974; Hinds et al., GCN 43977), with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the g, r, i, z, J, and Ks band starting at 2026-03-19T23:22:38 (9.77 days after the GRB trigger) and 2026-03-20T22:36:22 (10.74 after the GRB trigger). Unlike suggested by Becerra et al. (CGN 44059) we do not see signs of rebrightening in our observations in any filter (see also Volnova et al., GCN 44060). We thank Michael Schmidt and Silona Wilke for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44061. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42181] GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44060 SUBJECT: GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy DATE: 26/03/20 22:31:46 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> A. Volnova (IKI), N. Pankov (IKI), E. Klunko (ISTP), A. S. Moskvitin (SAO RAS), O. Spiridonova (SAO RAS), A. Pozanenko (IKI) report on behalf of GRB IKI FuN. We observed the field of GRB260310A/AT2026fgk detected by Fermi/GBM (Fermi GBM team, GCN 43951) and AstroSat(Salunke et al., GCN 43958) with AZT-33IK telescope of Mondy observatory. We obtained series in B and R filters starting on 2026-03-13. The OT discovered by GOTO (O'Neill et al. 2026, TNS Discovery Report 294132) and observed earlier (Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978;Martin-Carrillo et al., GCN 43979; Méndez et al., GCN 43980;de Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Pursiainen et al., GCN 43990; Becerra et al., GCN 43991; Li et al., GCN 43993; Jayaraman et al., GCN 43994; Stein et al., GCN 43996;Martin-Carrillo et al., GCN 44000; Moreno Méndez et al., GCN 43980; Becerra et al., GCN 43991; Li et al., GCN 43993; Stein et al., GCN 43996; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo et al., GCN 44003; Brivio et al., GCN 44004; Moskvitin et al., GCN 44006; Romanov, GCN 44020; Brosio et al., GCN 44021; Pawar et al., GCN 44022; Belkin et al., GCN 44043; Li et al., GCN 44044; Gupta et al., GCN 44051) is clearly detected in our images. Preliminary PSF photometry on some epochs is the following Date UT_start t_mid - T0, filter exp, mag err UL(3sigma) days s 2026-03-15 15:09:04 5.43535 15*120 B 19.18 0.05 23.0 2026-03-16 14:37:32 6.41345 15*120 B 19.05 0.05 22.6 2026-03-17 18:59:03 7.60549 30*120 B 19.18 0.05 22.7 2026-03-18 18:40:29 8.58565 19*120 B 19.47 0.06 21.7 2026-03-19 18:09:48 9.57128 30*120 B 19.61 0.06 23.2 2026-03-15 14:48:55 5.52493 11*120 R 18.27 0.05 23.0 2026-03-16 14:07:40 6.39202 13*120 R 18.22 0.05 22.8 2026-03-17 18:22:13 7.56948 15*120 R 18.29 0.06 22.8 2026-03-18 18:06:29 8.55786 15*120 R 18.60 0.06 22.4 2026-03-19 19:11:16 9.60355 15*120 R 18.71 0.07 22.7 The photometry is based on the nearby calibrations stars of PS1 catalogue converted to B, R using the Lupton (2005) transformations. The magnitudes are not corrected for Galactic extinctions. We do not observe the rebrightening reported in COLIBRÍ observations (Becerra et al., GCN 44059) up to the latest epoch (~9.6 days) in B,R - filters. Based on classification of the progenitor (Atteia et al., GCN 43981; Minaev et al., GCN 44053) we urge follow up observations to search for a supernova associated with GRB 260310A. View this GCN Circular online at https://gcn.nasa.gov/circulars/44060. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42180] GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44059 SUBJECT: GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening DATE: 26/03/20 20:08:08 GMT FROM: Rosa L. Becerra at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Rosa L. Becerra (UNAM), Camila Angulo (UNAM), Sarah Antier (IJCLAB), Noémie Globus (UNAM), Enrique Moreno Méndez (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Antonio de Ugarte Postigo (LAM), and Benjamin Schneider (LAM) report: We reimaged the field of AT 2026fgk, first reported by Hinds et al. (AstroNote 2026-65) and followed-up by a large number of facilities across multiple wavelengths (GCNs Circ. 43951, 43954, 43958, 43974, 43975, 43977, 43978, 43979, 43980, 43981, 43984, 43986, 43990, 43991, 43993, 43994, 43996, 44000, 44001, 44002, 44003, 44004, 44005, 44006, 44020, 44021, 44022, 44043, 44044, 44045, 44051, 44053, 44057, 44058), as a possible counterpart to the Fermi GBM GRB 260310A (Fermi GBM Team, GCN Circ. 43951; Humburg & Meegan, GCN Circ. 43975), and also detected by AstroSat CZTI (Salunke et al., GCN Circ. 43958), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed several epochs from 2026-03-20 03:35 to 11:21 UTC (from 9.94 to 10.27 days after the GRB trigger) in the g, r, and z filters. The data were reduced, coadded, calibrated, and analysed with the ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked images, we continue to detect AT 2026fgk. Compared with the photometry acquired on 2026-03-19, we observe a rebrightening in all three filters throughout the night, with a temporal index of alpha > 1.5. We encourage extended follow-up observations. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/44059. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42179] GRB 260310A/AT2026fgk: LBT near-infrared observations
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44058 SUBJECT: GRB 260310A/AT2026fgk: LBT near-infrared observations DATE: 26/03/20 17:40:46 GMT FROM: N. Passaleva at Sapienza University of Rome <niccolo.passaleva(a)uniroma1.it> Niccolo’ Passaleva, Yu-Han Yang, Narges Shahamt, Eleonora Troja (U Rome) report on behalf of the ERC BHianca team: Following the detection of GRB 260310A by Fermi/GBM and AstroSat CZTI (Fermi GBM team, GCN 43951,43975; AstroSat CZTI collaboration, GCN 43958), we observed the likely counterpart AT2026fgk (discovered by GOTO; O’Neill et al. 2026, TNS Discovery Report 294132) in J and K filters with the LUCI near-infrared imager mounted on the Large Binocular Telescope (LBT). Observations started at 2026-03-16T08:07:32 (~ 6.2 d after the GBM trigger) with an average airmass of 1.3. We detect the source with a preliminary magnitude of J~18.03 AB mag, calibrated using nearby stars from the 2MASS catalog (Skrutskie et al. 2006), uncorrected for Galactic extinction. Compared with previous near-infrared observations (Li et al., GCN 43993; Stein et al., GCN 43996; Brivio et al., GCN 44004), our measurement is consistent with a fading slope of 0.7. We acknowledge excellent support from the LBTO and LBT-INAF staff. View this GCN Circular online at https://gcn.nasa.gov/circulars/44058. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42178] NOEMA Detection of GRB 260310A
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44057 SUBJECT: NOEMA Detection of GRB 260310A DATE: 26/03/20 14:52:58 GMT FROM: Anna Y Q Ho at Cornell University <ayh24(a)cornell.edu> Anna Y. Q. Ho (Cornell), Michael Bremer (IRAM), Genevieve Schroeder (Cornell) report on behalf of a larger collaboration: On UT 2026 March 20 the NOrthern Extended Millimeter Array (NOEMA) observed the position of GRB 260310A / AT2026fgk (GCN 43951, 43958, 43974), a nearby (z=0.153; GCN 43977) gamma-ray burst with bright radio emission at cm wavelengths (GCN 44005, 44045). Observations were obtained in the new dual-band mode (100+230 GHz) as well as in Band 2 (150 GHz). With self-calibration, we measure a preliminary flux density of 17 mJy at 100 GHz, corresponding to a luminosity of 10^42 erg/s, typical for GRB afterglows at this epoch. Further observations are planned. We thank the NOEMA staff for rapidly approving and scheduling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44057. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42177] EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44056 SUBJECT: EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7 DATE: 26/03/20 10:46:01 GMT FROM: I. Perez-Garcia at Instituto de Astrofísica de Andalucía <ipg(a)iaa.es> I. Perez-Garcia, S.-Y. Wu, A. J. Castro-Tirado, E. J. Fernandez-Garcia, M.D. Caballero-Garcia, S. Guziy, G. Garcia-Segura, R. Sanchez-Ramirez (IAA-CSIC), Y.-D. Hu (INAF-OAB), C. Perez del Pulgar, A. Castellon, I. Carrasco (Univ. de Malaga), L. Hernandez-Garcia (Univ. de Valparaiso), M. Gritsevich (Univ. of Helsinki), D.-R. Xiong (Yunnan Observatories of CAS), 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-WXT trigger 01709258989 (Zhou et al. GCN 44054), the 0.6m BOOTES-7 robotic telescope at San Pedro de Atacama (Chile) responded to the alert on Mar. 20, 02:39 UT (i.e. 6-min after trigger, 1 min after notification). Within the reported EP-FXT error circle we find the star 1RXS J073101.9+460030 decreasing 0.9, 0.5 and 0.4 mag in g, r and i filters during a 20 min time interval, confirming EP-WXT trigger 01709258989 as due to a stellar flare. 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/44056. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42176] GRB 260318A: SVOM/GRM observation
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44055 SUBJECT: GRB 260318A: SVOM/GRM observation DATE: 26/03/20 06:30:30 GMT FROM: yzh807926(a)163.com SVOM/GRM team: Zheng-Hang Yu, Chao Zheng, Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Hui Yang (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 260318A (SVOM trigger reference: sb26031805) at 2026-03-18T22:36:00.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44049). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a precursor followed by a main episode with two peaks a T90 of 28.5 +7.0/-8.0 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260318A.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 303.6, DEC= 57.0 GCN#44049), is located at about 164 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-16 to T0+10 s is best fitted by a power law function. The power law index is -2.55 +0.17/-0.16. The event fluence (10-1000 keV) in this time interval is (6.72 +1.45/-1.02)E-05 erg/cm^2. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Zheng-Hang Yu(IHEP)(zhyu(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44055. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42175] The EP-WXT trigger 01709258989 is likely a flaring star
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44054 SUBJECT: The EP-WXT trigger 01709258989 is likely a flaring star DATE: 26/03/20 03:33:53 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H. Zhou, Y. Wang, Q. J. Huang (PMO, CAS), J. P. Chen (SYSU), H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709258989 at the time of 2026-03-20T02:33:39 UTC, EP-FXT performed an automatic follow-up observation, and detected a source at RA: 112.7520 deg, Dec: 46.0075 deg, is likely a stellar flare associated with 1RXS J073101.9+460030. The estimated flux of the flare is around 1.0 x 10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 3.6 x 10^31 erg/s. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44054. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42174] GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44053 SUBJECT: GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90 DATE: 26/03/20 01:38:39 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> P. Minaev (IKI) , A. Pozanenko (IKI) on behalf of GRB follow-up team We analyzed GRB 260310A (Hamburg et al., GCN 43975; Salunke et al., GCN 43958; Atteia et al., GCN 43981) using publicly available data of GBM/Fermi. The burst consists of several emission episodes with a total duration of T_90 = 86 s. Time integrated energy spectrum, constructed in the time interval (-4, 70) s since GBM trigger, is best described by Band model with E_p = 175 keV and fluence F = 1.74e-5 erg cm^-2 in 1 keV - 10 MeV range. Using z = 0.153 (Hinds et al., GCN 43977; de Ugarte Postigo et al., GCN 43984) we obtain E_iso = 9.8e50 erg. GRB 260310A is placed above the correlation fit for type II (long) bursts on Ep,i – Eiso diagram, as mentioned in (Atteia et al., GCN 43981), but it is inside 2 sigma correlation regions for both type I (short) and type II (long) bursts, therefore we cannot consider it as a clear outlier. Indeed, at the EH – T_90,i diagram (see [1-2] for details) GRB 260310A is well classified as type II (long) burst. The Ep,i – Eiso and EH - T90,i diagrams can be found at https://heaiki.ru/lvc/GRB260310A/ [1] - Minaev et al., MNRAS, 492, 1919, 2020 [2] - Minaev et al., Astronomy Letters, 46, 9, 573, 2020 View this GCN Circular online at https://gcn.nasa.gov/circulars/44053. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42173] GRB 260318A: GECAM-B observation
by GCN Circulars 19 Mar '26

19 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44052 SUBJECT: GRB 260318A: GECAM-B observation DATE: 26/03/19 15:47:49 GMT FROM: yzh807926(a)163.com Zheng-Hang Yu, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by GRB 260318A, at 2026-03-18T22:35:52.600 UTC (denoted as T0), which is also detected by Fermi/GBM ((Fermi GBM team, GCN #44049). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 19.5 +3.0/-2.5 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260318A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/44052. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42172] GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
by GCN Circulars 19 Mar '26

19 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44051 SUBJECT: GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT DATE: 26/03/19 14:57:05 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180(a)gmail.com> Anshika Gupta, Kumar Pranshu, Dhruv Jain, Debalina Kar, Pankaj Pawar, and Kuntal Misra (ARIES) report: We observed the field of GRB260310A/AT2026fgk detected by Fermi/GBM (Fermi GBM team, GCN 43951) and AstroSat(Salunke et al., GCN 43958) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations began on 2026-03-17 at 20:33:36.00 UT, i.e., ~ 7.65 days after the Fermi/GBM trigger. We have taken multiple frames with an exposure time of 300s in the I filter. We stacked the images after the alignment. We detect an optical afterglow in our stacked image. We obtain the following preliminary magnitude in the stacked image: Date Start_UT T_start-T0 (days) Filter Exp time (s) Magnitude ================================================================ 2026-03-17 20:33:36.00 ~7.65 I 300s*3 18.01 +/-0.02 The optical detection of the burst is consistent with Lipunov et al., GCN 43954; Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979, 44000; Moreno Méndez et al., GCN 43980; Becerra et al., GCN 43991; Li et al., GCN 43993; Stein et al., GCN 43996; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo et al., GCN 44003; Brivio et al., GCN 44004; Moskvitin et al., GCN 44006; Romanov, GCN 44020; Brosio et al., GCN 44021; Pawar et al., GCN 44022; Belkin et al., GCN 44043; Li et al., GCN 44044. The magnitude is not corrected for the Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the USNO-B1.0 catalogue. View this GCN Circular online at https://gcn.nasa.gov/circulars/44051. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42171] Fermi GRB 260318A: Global MASTER-Net observations report
by GCN Circulars 18 Mar '26

18 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44050 SUBJECT: Fermi GRB 260318A: Global MASTER-Net observations report DATE: 26/03/18 23:00:55 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260318A ( Fermi GBM team, GCN 44049) errorbox 572 sec after notice time and 596 sec after trigger time at 2026-03-18 22:45:44 UT, with upper limit up to 18.1 mag. The observations began at zenith distance = 62 deg. The sun altitude is -43.5 deg. The galactic latitude b = 12 deg., longitude l = 92 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3194853 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 657 | 2026-03-18 22:45:44 | MASTER-Kislovodsk | (20h 14m 11.39s , +56d 41m 32.7s) | P| | 120 | 17.6 | 797 | 2026-03-18 22:48:04 | MASTER-Kislovodsk | (20h 14m 11.18s , +56d 41m 32.8s) | P| | 120 | 17.4 | 938 | 2026-03-18 22:50:25 | MASTER-Kislovodsk | (20h 14m 11.08s , +56d 41m 36.1s) | P| | 120 | 18.1 | 1078 | 2026-03-18 22:52:45 | MASTER-Kislovodsk | (20h 14m 11.06s , +56d 41m 40.9s) | P| | 120 | 18.0 | The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44050. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42170] GRB 260318A: Fermi GBM Final Real-time Localization
by GCN Circulars 18 Mar '26

18 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44049 SUBJECT: GRB 260318A: Fermi GBM Final Real-time Localization DATE: 26/03/18 22:46:23 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 22:35:47 UT on 18 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260318A (trigger 795566152.456906 / 260318942). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 303.6, Dec = 57.0 (J2000 degrees, equivalent to J2000 20h 14m, 57d 00'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 17.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260318942/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260318942/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260318942/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44049. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42169] IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
by GCN Circulars 18 Mar '26

18 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44048 SUBJECT: IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility DATE: 26/03/18 18:09:53 GMT FROM: Jannis Necker at DESY <jannis.necker(a)desy.de> Akshay Eranhalodi (DESY), Robert Stein (JSI), Jannis Necker (Leiden University), and Anna Franckowiak (Ruhr University Bochum) report, On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: As part of the ZTF neutrino follow up program (Stein et al. 2023), we observed the localization region of the neutrino event IceCube-260315A (Zegarelli et. al, GCN 44017) with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the g- and r-band beginning at 2026-03-15 07:45 UTC, approximately 5.4 hours after event time. We covered 93.7% (0.7 sq deg) of the reported localization region. This estimate accounts for chip gaps. Each exposure was 300s with a typical depth of 21.0 mag. The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019) . No candidate counterparts were detected. We do not recover the previously reported candidate counterpart AT 2026fpm (Lipunov et al. 2026, GCN 44023) because it lies outside of the 90% contianment area based on the publicly available probability map of the neutrino event localisation. As the source is also likely a known variable (Fortin et al. 2026, GCN 44026; Feng et al., GCN 44042) it is unlikely to be the neutrino counterpart. ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan; OKC, Sweden; DZA, Germany. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert database searches are done by AMPEL (Nordin et al. 2019). Alert filtering is performed with the nuztf (Stein et al. 2021, https://github.com/desy-multimessenger/nuztf ). View this GCN Circular online at https://gcn.nasa.gov/circulars/44048. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42168] Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
by GCN Circulars 18 Mar '26

18 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44047 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB DATE: 26/03/18 15:31:39 GMT FROM: oliver.roberts(a)universityofgalway.ie O.J. Roberts (Uni. of Galway, Ireland) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger GRB 260313A (trigger 795096033/260312500) at 12:00:28.58 UT on 13 March 2026, tentatively classified as a GRB (GCN 43995, GCN 43987), is in fact unlikely to be a GRB. The nature of this trigger is uncertain." View this GCN Circular online at https://gcn.nasa.gov/circulars/44047. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42167] GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
by GCN Circulars 18 Mar '26

18 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44046 SUBJECT: GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate DATE: 26/03/18 12:06:23 GMT FROM: F. Fortin at IRAP <ffortin.sci.edu(a)gmail.com> Francis Fortin (IRAP), Diego López-Cámara (UNAM), Jean-Grégoire Ducoin (CPPM), Antonio de Ugarte Postigo (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Missimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM) and Benjamin Schneider (LAM) report: We imaged the field of the GRB 260316A / EP260316a (Jiang et al., GCN Circ. 44027, GCN Circ. 44034) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-18 07:20:28 to 09:50:38 UTC (from 42.8 to 45.3 hours after the trigger) and obtained 111 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025) and the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We still detect the optical counterpart candidate that we previously reported in Fortin et al., GCN Circ. 44037. Template subtraction from 2026-03-17 to 2026-03-18 shows no significant residuals between the two epochs, and therefore does not allow us to conclude on the potential variability of this source. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/44046. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42166] GRB 260310A / AT 2026fgk: radio detection with the VLA
by GCN Circulars 18 Mar '26

18 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44045 SUBJECT: GRB 260310A / AT 2026fgk: radio detection with the VLA DATE: 26/03/18 09:14:01 GMT FROM: Stefano Giarratana at INAF-OAB <s.giarratana(a)ira.inaf.it> S. Giarratana (INAF-OAB), M. Giroletti (INAF-IRA), G. Ghirlanda (INAF-OAB), N. Di Lalla (Stanford Univ.), N. Omodei (Stanford Univ.), O. S. Salafia (INAF-OAB), L. Nava (INAF-OAB) At 10:22:44 UT on 2026 March 14 (T_mid = 4.26 days post-burst) the Karl G. Jansky VLA observed the field of GRB 260310A / AT 2026fgk (Fermi GBM team, GCN 43951, 43975; AstroSat CZTI collaboration, GCN 43958) in three bands, with central frequencies of 6, 10 and 15 GHz. The standard 3C286 was used as bandpass and flux density calibrator, while J1435+7605 served as phase calibrator. From a preliminary analysis, an unresolved radio source (Rhodes et al., GCN 44005) is clearly detected at all frequencies at a position: RA: 14:37:16.1424 +- 0.001 Dec: +71:50:30.328 +- 0.01 consistent with the X-ray (Jayaraman et al., GCN 43994) and optical (Hinds et al., AstroNote 2026-65, GCN 43977; Konno et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979, 44000; Moreno Méndez et al, GCN 43980; Becerra et al., GCN 43991; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo et al., GCN 44003; Moskvitin et al., GCN 44006; Romanov, GCN 44020; Brosio et al., GCN 44021; Pawar et al., GCN 44022) and infrared (Li et al., GCN 43993; Stein et al., GCN 43996; Brivio et al., GCN 44004) position of the transient. The preliminary analysis yields the following results: ================================================================ T_mid Freq Peak r.m.s. Beam PA [days] [GHz] [uJy/b] [uJy/b] [arcsec^2] [deg] ================================================================ 4.26 6 3894 8 0.39x0.29 -31 4.26 10 6368 13 0.24x0.19 3.9 4.26 15 9104 29 0.16x0.11 -11 ================================================================ We would like to thank the staff of the VLA for approving, executing, and processing the observations. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. These observations were carried out as part of project SF181027, approved in the framework of the Fermi - NRAO joint program agreement. View this GCN Circular online at https://gcn.nasa.gov/circulars/44045. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42165] GRB 260310A / AT2026fgk: SVOM/VT optical observations
by GCN Circulars 18 Mar '26

18 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44044 SUBJECT: GRB 260310A / AT2026fgk: SVOM/VT optical observations DATE: 26/03/18 07:47:29 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, Y. N. Ma, C. Wu, Z. H. Yao, Y. L. Qiu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. T. Palmerio (CEA/Irfu)，J. X. Cao (GXU) report on behalf of the SVOM/VT team. SVOM/VT performed several ToO observations of the field of GRB 260310A detected by Fermi (Fermi GBM team, GCN 43951) and AstroSat(Salunke et al., GCN 43958) from 2026-03-14 to 2026-03-17 in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The reported optical counterpart AT2026fgk discovered by GOTO(O'Neill et al. 2026, TNS Discovery Report 294132) and observed by other observatories (Lipunov et al., GCN 43954; Konno et al., GCN 43974, Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979, Moren Méndez et al., GCN 43980; de Ugarte Postigo et al., GCN 43984, Pursiainen et al., Becerra et al., GCN 43991; Martin-Carrillo et al., GCN 44000; Watson et al., GCN 44001; Lai et al., GCN 44002; L. Izzo, GCN 44003; Brivio et al., GCN 44004; Rhodes et al., GCN 44005; Moskvitin et al., GCN 44006; Brosio et al., GCN 44021; Pawar et al., GCN 44022; Belkin and Shrestha, GCN 44043) is clearly detected in single frames in both channels. The preliminary measurements in AB magnitudes are given below: Mid_time Band Exposure Time Magnitude (AB) 5.26 day VT_R 70 sec 18.44 +/- 0.05 mag 5.26 day VT_B 70 sec 18.94 +/- 0.05 mag 7.35 day VT_R 70 sec 18.65 +/- 0.05 mag 7.35 day VT_B 70 sec 19.15 +/- 0.05 mag Our photometry was not corrected for Galactic extinction. 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/44044. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42164] GRB 260310A / AT2026fgk: LCO optical observations
by GCN Circulars 18 Mar '26

18 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44043 SUBJECT: GRB 260310A / AT2026fgk: LCO optical observations DATE: 26/03/18 06:59:09 GMT FROM: Sergey Belkin at Monash University <sergey.belkin(a)monash.edu> S. Belkin and M. Shrestha (Monash U) report: We observed the optical counterpart AT2026fgk of GRB 260310A, detected by Fermi/GBM (Fermi GBM Team, GCN 43951) and AstroSat/CZTI (Salunke et al., GCN 43958), with the Las Cumbres Observatory 1m telescope at McDonald Observatory equipped with the Sinistro instrument. Observations began on 2026-03-14 at 06:12:09 UT, approximately 4.05 days after the trigger. We obtained 4 x 60 s exposures in the r band and 6 x 60 s exposures in the u band. In the stacked images we clearly detect the reported optical counterpart AT2026fgk (e.g. Lipunov et al., GCN 43954; Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979; Moreno Mendez et al., GCN 43980; de Ugarte Postigo et al., GCN 43984; Pursiainen et al., GCN 43990; Becerra et al., GCN 43991; Martin-Carrillo et al., GCN 44000; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo, GCN 44003; Moskvitin et al., GCN 44006; Romanov, GCN 44020; Brosio et al., GCN 44021; Pawar et al., GCN 44022), discovered by GOTO (O’Neill et al., TNS Discovery Report 294132). The preliminary photometry from the stacked images is: Date (UT) T-T0 (days) Filter Exp. time (s) Magnitude 3-sigma UL ======================================================================================== 2026-03-14 06:14:13 4.0535 r 60 x 4 18.58 +/- 0.02 21.79 2026-03-14 06:21:49 4.0588 u 60 x 6 19.47 +/- 0.04 21.12 The r-band photometry is calibrated against Pan-STARRS field stars. The u-band photometry is calibrated against Gaia DR3 synthetic SDSS u-band stars. The quoted values are not corrected for Galactic extinction. Further follow-up is encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/44043. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42163] IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
by GCN Circulars 18 Mar '26

18 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44042 SUBJECT: IceCube-260315A/AT2026fpm: EP-FXT follow-up observation DATE: 26/03/18 04:57:04 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. P. Feng, B. Zhang (USTC), H. N. Yang, Y. Liu (NAO, CAS) The Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) performed a follow-up observation of AT2026fpm (Segura et al., GCN 44023) at UTC 2026-03-16T23:31:53 (T0+45.21h) (The IceCube Collaboration, GCN 44017). An X-ray source was detected at R.A. = 176.1586 deg, DEC = -2.6035 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic) and the flux of 1.1×10^(-13) erg/s/cm^2 in 0.5-10 keV band. The X-ray position is consistent with the optical transient AT2026fpm, which is spatially consistent with a QSO at z=1.389. 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/44042. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42162] GRB 260317A: Fermi GBM Final Localization
by GCN Circulars 17 Mar '26

17 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44041 SUBJECT: GRB 260317A: Fermi GBM Final Localization DATE: 26/03/17 21:55:00 GMT FROM: rhamburg(a)usra.edu The Fermi GBM team reports the detection of a likely SHORT GRB. "At 20:01:51.98 UT on 17 March 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260317A (trigger 795470516/260317835). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 255.62, Dec = -18.51 (J2000 degrees, equivalent to J2000 17h 2m, -18d 30'), with a statistical uncertainty of 13.33 degrees. The angle from the Fermi LAT boresight is 93 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260317835/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260317835/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260317835/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44041. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42161] GRB 260316A: GECAM-B observation
by GCN Circulars 17 Mar '26

17 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44040 SUBJECT: GRB 260316A: GECAM-B observation DATE: 26/03/17 15:46:38 GMT FROM: Yue Wang <m18509381757(a)163.com> Yue Wang, Chao Zheng, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by GRB 260316A at 2026-03-16T17:12:53.100 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44031) and SVOM/GRM (Yue Wang et. al., GCN #44039). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a single pulse with a duration (T90) of 2.4 +0.4/-0.4 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260316A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/44040. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42160] GRB 260316A: SVOM/GRM observation
by GCN Circulars 17 Mar '26

17 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44039 SUBJECT: GRB 260316A: SVOM/GRM observation DATE: 26/03/17 15:43:47 GMT FROM: Yue Wang <m18509381757(a)163.com> SVOM/GRM team: Yue Wang, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Sebastien Guillot, Hui Yang (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 260316A at 2026-03-16T17:12:54.000 (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44031). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 1.6 +1.6/-0.8 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260316A.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 305.5, Dec = -79.3, Error = 3.2, GCN #44031), is located at about 113 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-1.2 to T0+0.6 s is best fitted by a power law function. The power law index is -2.23 +0.17/-0.16. The event fluence (10-1000 keV) in this time interval is (3.21 +0.50/-0.51)E-06 erg/cm^2. 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: Yue Wang (IHEP) (yuewang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44039. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42159] EP260316a / GRB 260316A: SVOM/VT optical upper limits
by GCN Circulars 17 Mar '26

17 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44038 SUBJECT: EP260316a / GRB 260316A: SVOM/VT optical upper limits DATE: 26/03/17 15:21:28 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, Y. N. Ma, C. Wu, Z. H. Yao, Y. L. Qiu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. T. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observation of the field of EP260316a detected by Einstein Probe (Jiang et al., GCN 44027, GCN 44034), and GRB 260316A with the sub-threshold detection by Fermi (Ravasio et al., GCN 44029). The observation started at 2026-03-16T22:31:53 UTC, i.e., about 9.98 hours post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. No uncatalogued optical source was detected in our stacked images. The 3-sigma upper limits are: Mid_time Band Exposure Time Magnitude (AB) 10.35 hour VT_R 37*70 sec > 23.2 mag 10.35 hour VT_B 39*70 sec > 23.3 mag The faint optical candidate reported by COLIBRÍ (Fortin et al., GCN 44037) was not detected in our stacked images. 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/44038. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42158] EP260316a: COLIBRÍ faint optical counterpart candidate
by GCN Circulars 17 Mar '26

17 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44037 SUBJECT: EP260316a: COLIBRÍ faint optical counterpart candidate DATE: 26/03/17 13:06:02 GMT FROM: F. Fortin at IRAP <ffortin.sci.edu(a)gmail.com> Francis Fortin (IRAP), Fredd Sánchez Álvarez (UNAM), Jean-Luc Atteia (IRAP), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Missimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the EP260316a (Jiang et al., GCN Circ. 44027, GCN Circ. 44034), also detected by Fermi (Ravasio et al., GCN Circ. 44029) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-17 07:56:51 to 10:00:54 UTC (from 19.4 to 21.5 hours after the trigger) and obtained 94 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detect a faint (SNR = 5.7) uncatalogued source located at the edge of the EP/FXT 10 arcsec error circle (Jiang et al., GCN Circ. 44034) at: RA(J2000) = 15:07:55.62 = 226.98176 degrees Dec(J2000) = +27:26:53.9 = +27.44830 degrees with an uncertainty of 0.5 arcsec. The preliminary magnitude derived for that source is: r = 24.40 +/- 0.19 z > 23.38 (3-sigma) We note that our images are deeper than the PS1 and LS catalogues, hence we cannot fully conclude whether or not this source is a transient. Further observations are planned. Followup of this source with other facilities is also encouraged. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/44037. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42157] Fermi-LAT Gamma-ray Observations of IceCube-260315A
by GCN Circulars 17 Mar '26

17 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44036 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-260315A DATE: 26/03/17 12:07:57 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg) and 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 IC260315A neutrino event (GCN 44017) 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 26-03-15 at 02:19:06.60 UTC (T0) with J2000 position RA = 175.69 (+0.49, -0.46) deg, Decl. = -1.90 (+0.53, -0.51) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC260315A localization error (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, 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 (>5sigma) new excess emission (> 100 MeV) within the IC260315A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC260315A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 2.7e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), <1.6e-08 (<5.0e-08) 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 source 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/44036. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42156] GRB 260316A: AstroSat CZTI detection
by GCN Circulars 17 Mar '26

17 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44035 SUBJECT: GRB 260316A: AstroSat CZTI detection DATE: 26/03/17 09:51:41 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> Harsha K. H. (IUCAA), M. Tembhurnikar (IUCAA), S. Salunke (IUCAA), A. Arya (IITB), A. Goyal (IITB), G. Waratkar (Caltech/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 GRB 260316A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 44031), Calet (Trigger Num. 1457716347), and SVOM (Trigger Num. sb26031602). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-03-16 17:12:53.75 UTC. The measured peak count rate associated with the burst is 524 (+158, -53) counts/s above the background in the combined data of all quadrants, with a total of 818 (+139, -151) counts. The local mean background count rate was 306 (+5, -8) counts/s. Using cumulative rates, we measure a T90 of 4.91 (+1.7, -2.5) s. The source was also faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. 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/44035. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42155] EP260316a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 17 Mar '26

17 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44034 SUBJECT: EP260316a: refined analysis of the EP-WXT and EP-FXT observations DATE: 26/03/17 08:21:17 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S. Q. Jiang (NAO, CAS), B. Zhang, J. P. Feng (USTC), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260316a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Jiang et al., GCN 44027). The transient was detected immediately when WXT observation started at T0=2026-03-16 12:32:52. The WXT observation lasted for approximately 22 seconds, and was interrupted due to the autonomous follow-up observation. The WXT light curve exhibits a double-peaked structure, which is also observed in the Fermi/GBM data (Ravasio et al., GCN 44029). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a hydrogen column density of 2.4 (-1.1/+1.4) × 10^22 cm^-2 and a photon index of 2.9 (-1.4/+1.6). The derived average unabsorbed 0.5-4 keV flux is 3.1 (-2.1/+9.1) × 10^(-8) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously at 2026-03-16 12:35:40 (UTC, T0+168 s). The exposure time of this observation is 5.4 ks. On-ground analysis of the FXT data found an uncatalogued fading source at R.A., Dec. = 226.9819, 27.4455 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the WXT position. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a hydrogen column density of 7.01 (-0.55/+0.57) × 10^21 cm^-2 and a photon index of 2.39 (-0.10/+0.11). The derived average unabsorbed 0.5-10 keV flux is 9.51 (-0.41/+0.47) × 10^(-12) erg/s/cm^2. A follow-up observation with the EP/FXT was planned, and further information will be updated when the telemetry data are received. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44034. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42154] IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44033 SUBJECT: IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube DATE: 26/03/16 17:57:13 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-260315A (https://gcn.nasa.gov/circulars/44017) in a time range of 1000 seconds centered on the alert event time (2026-03-15 02:10:46.630 UTC to 2026-03-15 02:27:26.630 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-260315A. We report a p-value of 1.00 in this time window. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.5e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260315A 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 3e+02 GeV and 2e+05 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2026-03-14 02:19:06.630 UTC to 2026-03-16 02:19:06.630 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.6e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260315A 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/44033. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42153] EP260316a: Xinglong optical upper limit
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44032 SUBJECT: EP260316a: Xinglong optical upper limit DATE: 26/03/16 17:46:14 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Junbo-Zhang (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Feng-Xiao (NAOC), Yuguang-Sun (NAOC), Jie-Zheng (NAOC), Dong-Xu (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration: Following the detection of EP260316a by EP-WXT (Jiang et al., GCN 44027), we observed the field of EP260316a using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 6x300s clear-band frames with a median time of 2026-03-16 16:18:40 (UT), 3.76 hr after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 3 arcmin EP/WXT error circle (Jiang et al., GCN 44027), down to 3-sigma limiting magnitudes of g ~22.00 mag, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle. We also detected no optical transient candidate with a median time of 2026-03-16T16:37:50.536 (UT) with the 0.8-m Telescope in Xinglong, Hebei, China. The upper limit is ～19.9 mag in the g-band. View this GCN Circular online at https://gcn.nasa.gov/circulars/44032. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42152] GRB 260316A: Fermi GBM Final Real-time Localization
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44031 SUBJECT: GRB 260316A: Fermi GBM Final Real-time Localization DATE: 26/03/16 17:23:26 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 17:12:52 UT on 16 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260316A (trigger 795373977.681026 / 260316717). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 305.5, Dec = -79.3 (J2000 degrees, equivalent to J2000 20h 22m, -79d 17'), with a statistical uncertainty of 3.2 degrees. The angle from the Fermi LAT boresight is 81.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260316717/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260316717/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260316717/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44031. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42151] EP260316a: optical upper limit with Kinder observations
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44030 SUBJECT: EP260316a: optical upper limit with Kinder observations DATE: 26/03/16 17:12:28 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> M.-H. Lee, A. Aryan, T.-W. Chen, H.-Y. Hsiao (all NCU), A. K. H. Kong (NTHU), J. H. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), Y.-H. Lee, A. Sankar.K, C.-H. Lai, Y.-C. Pan, C.-C. Ngeow, W.-J. Hou, C.-S. Lin, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz, and M. Huber (both IfA, Hawaii) report: We observed the field of the EP260316a (Jiang et al., GCN 44027) using the 1m LOT at the Lulin observatory, as part of the Kinder collaboration (Chen et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first LOT epoch of observations in g-band started at 14:11 UTC on 16th of March 2026 (MJD 61115.591), 1.63 hr after the EP-WXT detection. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. Neither in the stacked nor in the difference image did we detect any signature of a new or uncatalogued source within the EP-FXT localization circle (20"). Moreover, we further used AutoPhOT to perform PSF photometry. The details of the observations and the 3-sigma upper limit (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude| avg. Seeing | Med. Airmass LOT | g | 61115.591 | 1.63 | 300 * 12 | >23.2 | 1".52 | 1.94 The presented magnitudes are calibrated using the field stars from the ATLAS-refcat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105). The reported upper limit is not corrected for an expected galactic extinction of A_r = 0.12 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/44030. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42150] EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44029 SUBJECT: EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection DATE: 26/03/16 17:06:07 GMT FROM: mariaedvige.ravasio(a)ru.nl M. E. Ravasio (ICE-CSIC and Radboud Univ.), P.G. Jonker (Radboud Univ.) and E. Burns (LSU), R. Hamburg (USRA), and P. Veres (UAH) report on behalf of the Fermi-GBM Team: Fermi-GBM had full spatial and temporal coverage of the transient EP260316a detected by EP-WXT (EP Team GCN 44027). There was no Fermi-GBM onboard trigger around the corrected EP starting time at T0 = 2026-03-16T12:33:13 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 T0, seeking signals between 64 ms and 32.768 s in duration. A faint transient signal was found most significantly at ~T0-3.6 s on a 4 s timescale, with a false alarm rate of 6.5e-05 Hz, although there is evidence of an earlier start of the emission at T0-20 s. The localisation is consistent with the EP one, with a spatial association probability of 98.8%. Among the three spectral templates tested, the transient was best-fit with a“soft” spectral template (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/44029. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42149] GRB 260314A: Glowbug gamma-ray detection
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44028 SUBJECT: GRB 260314A: Glowbug gamma-ray detection DATE: 26/03/16 16:43:10 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260314A, which was also detected by Fermi/GBM (GCN 43997) and GECAM-B (GCN 44008). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-03-14 00:58:49.312 with a duration of 6.1 s and a total significance of about 16.5 sigma. The detection occurred during a time of high background. The light curve comprises a single peak at ~T0+3s. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44028. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42148] The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44027 SUBJECT: The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up DATE: 26/03/16 14:23:30 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S. Q. Jiang (NAO, CAS), B. Zhang, J. P. Feng (USTC), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: The trigger time reported in the notice for EP-WXT alert 00199258890 is incorrect. The correct trigger time is 2026-03-16T12:33:13.451 (UTC), rather than 2026-03-16T20:33:13.451 (UTC). The X-ray transient was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260316a. The transient triggered EP-WXT (ID: 00199258890) at 2026-03-16T12:33:13.451 (UTC). The WXT position of the source is R.A. = 226.983 deg, DEC = 27.466 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 226.9840 deg, DEC = 27.4447 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. 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/44027. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42147] IceCube-260315A: COLIBRÍ optical observations
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44026 SUBJECT: IceCube-260315A: COLIBRÍ optical observations DATE: 26/03/16 13:05:38 GMT FROM: F. Fortin at IRAP <ffortin.sci.edu(a)gmail.com> IceCube 260315A: COLIBRÍ optical observations Francis Fortin (IRAP), Leonardo García García (UNAM), Jean-Grégoire Ducoin (CPPM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Missimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of IceCube 260315A (The IceCube Collaboration, GCN Circ. 44017) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-16 06:23:48 to 09:13:24 UTC (from 28 to 30.9 hours after the trigger) and obtained 63 minutes of exposure in the g, r filters, and 126 minutes in the z filter. The data were reduced, coadded and analyzed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detected the optical counterpart candidate AT 2026fpm reported by Segura et al., GCN Circ. 44023, at a preliminary magnitude of: g = 19.94 +/- 0.01 r = 19.69 +/- 0.01 z = 19.66 +/- 0.01 The optical counterpart candidate lies on top of a catalogued source in the Legacy Survey with magnitudes of: g = 21.04 r = 20.59 z = 20.48 However, this LS source is flagged as variable. We also note that it is found in PS1 at a much fainter level. This would indicate that AT 2026 fpm is a known variable source. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/44026. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42146] EP260314a: Xinglong optical upper limit
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44025 SUBJECT: EP260314a: Xinglong optical upper limit DATE: 26/03/16 13:00:42 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Junbo-Zhang (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Feng-Xiao (NAOC), Jie-Zheng(NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration: Following the detection of EP260314a by EP-WXT (Zhao et al., GCN 44010; Wu et al., GCN 44016), we observed the field of EP260314a using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 3x600s clear-band frames with a median time of 2026-03-15 17:58:07 (UT), 19.11 hr after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 3 arcmin EP/WXT error circle (Zhao et al., GCN 44010; Wu et al., GCN 44016), down to 3-sigma limiting magnitudes of g ~21.5, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle. View this GCN Circular online at https://gcn.nasa.gov/circulars/44025. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42145] EP260314a: optical upper limit with Kinder observations
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44024 SUBJECT: EP260314a: optical upper limit with Kinder observations DATE: 26/03/16 10:31:28 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> C.-H. Lai, A. Aryan, Y.-H. Lee, C.-S. Lin, T.-W. Chen (all NCU), A. K. H. Kong (NTHU), J. H. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), A. Sankar.K, M.-H. Lee, Y.-C. Pan, C.-C. Ngeow, W.-J. Hou, H.-Y. Hsiao, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz, and M. Huber (both IfA, Hawaii) report: We observed the field of the EP260314a (Zhao et al., GCN 44010; Wu et al., GCN 44016) using the 1m LOT at the Lulin observatory, as part of the Kinder collaboration (Chen et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first LOT epoch of observations in g-band started at 16:09 UTC on 15th of March 2026 (MJD 61114.673), 17.52 hr after the EP-WXT detection. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. Neither in the stacked nor in the difference image did we detect any signature of the optical counterpart candidate reported by Li et al., (GCN 44013). Moreover, we further used AutoPhOT to perform PSF photometry. The details of the observations and the 3-sigma upper limit (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude| avg. Seeing | Med. Airmass LOT | r | 61114.673 | 17.52 | 300 * 6 | >22.8 | 1".31 | 1.81 Our upper limit is consistent with previously reported non-detections (Lipunov et al., GCN 44014; Pérez-García et al., GCN 44015; Fortin et al., GCN 44019). The presented magnitudes are calibrated using the field stars from the ATLAS-refcat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105). The reported upper limit is not corrected for an expected galactic extinction of A_r = 0.16 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/44024. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42144] IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44023 SUBJECT: IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate DATE: 26/03/15 18:39:46 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> M.J. Segura, C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), Ya.Kechin, V.Lipunov (Lomonosov MSU), N.Budnev, O.Gress (ISU), A.Kuznetsov, I.Panchenko, P.Balanutsa, G.Antipov, E.Gorbovskoy, N.Tiurina, V.Senik, A.Chasovnikov, M.Shilova,V.Topolev, D.Vlasenko, A.Sankovich, Yu.Tselik (Lomonosov MSU), D.Svinkin (Ioffe Institute), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), 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, J.Tanori, L. Villalobos, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) MASTER OT J114437.99-023613.5/AT 2026fpm discovery MASTER-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) was pointed to the IceCube Alert 260315A (trigger No 46886533,11h 42m 40.32s , -01d 53m 06.0s, R=0.71) errorbox 105 sec after notice time and 224 sec after trigger time at 2026-03-15 02:22:50 UT, with upper limit up to 20.4 mag. The observations began at zenith distance = 45 deg. The sun altitude is -42.8 deg. The galactic latitude b = 57 deg., longitude l = 272 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3187113 MASTER-OAFA auto-detection system [4] discovered OT source at (RA, Dec) = 11h 44m 37.99s -02d 36m 13.5s on 2026-03-15.10943 UT very close to center of neutrino errorbox (GCN Circular #44017). The OT magnitude in 'CLEAR' filter is 19.2m (mlim = 20.0). The OT is seen in 44 images. There is no minor planet at this place. We have reference image on 2026-02-12.28608 UT with 'FAULT' filter 19.9m. Spectral observations are required. The discovery and reference images are available at: http://master.sai.msu.ru/static/OT/114437.99-023613.5.png [1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L [2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271 [3] Lipunov et a. 2019, ARep, vol.63, 293 [4] Lipunov et al. 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics,Lomonosov MSU PRESS, 591pp. http://www.pereplet.ru/lipunov/625.html#625 View this GCN Circular online at https://gcn.nasa.gov/circulars/44023. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42143] GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44022 SUBJECT: GRB 260310A / AT2026fgk: 1.3m DFOT optical observations DATE: 26/03/15 17:21:19 GMT FROM: pawarpankaj1492(a)gmail.com Pankaj Pawar, Debalina Kar, Anshika Gupta, Dhruv Jain and Kuntal Misra (ARIES) report: We observed the likely optical counterpart of GRB 260310A, detected by Fermi/GBM(Fermi/GBM team, GCN 43951) and AstroSat(Salunke et al., GCN 43958), with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations began on 2026-03-14 at 18:29:38 UT, approximately 109.54 hours (~4.56 days) after the trigger. The reported optical couterpart AT2026fgk (Lipunov et al., GCN 43954; Konno et al., GCN 43974, Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979, Moren Méndez et al., GCN 43980; de Ugarte Postigo et al., GCN 43984, Pursiainen et al., Becerra et al., GCN 43991; Martin-Carrillo et al., GCN 44000; Watson et al., GCN 44001; Lai et al., GCN 44002; L. Izzo, GCN 44003; Brivio et al., GCN 44004; Rhodes et al., GCN 44005; Moskvitin et al., GCN 44006; Brosio et al., GCN 44021) is clearly detected in a single 100s R-band frame. We derive the following magnitude from the stacked image: Date Start_UT T_start-T0(days) Filter Exp time (s) Magnitude =============================================================== 2026-03-14 18:29:38 ~4.56 R 100s*1 18.54 ± 0.12 The reported magnitude is calibrated using Pan-STARRS field stars and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44022. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42142] GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44021 SUBJECT: GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations DATE: 26/03/15 16:12:58 GMT FROM: A. Brosio at ABObservatory Rosarno <antonino.brosio(a)gmail.com> A. Brosio (ABObservatory Rosarno), M. A. Tripodi (ABObservatory Rosarno), S. Savaglio (Università della Calabria), S. Benatti, M. G. Guarcello (INAF - Osservatorio Astronomico di Palermo), M. Basilicata, L. Cabona, M. Rainer, F. M. Zerbi (INAF - Osservatorio Astronomico di Brera), G. Bracco, P. Cianfarra, L. Sangaletti, S. Tosi, S. Zappatore (Università di Genova), A. Di Dato (INAF - Osservatorio Astronomico di Capodimonte), D. Liguori (Osservatorio "G. Galilei", Liceo Scientifico Cariati), S. Masiero, A. Nastasi (GAL Hassin, Isnello), R. Nesci (Associazione Astronomica Antares APS di Foligno), L. Betti, E. Pace, R. Stanga (Università di Firenze), D. Ricci (INAF - Osservatorio Astronomico di Padova) for the NOCTIS team report We observed the transient AT 2026fgk, proposed as the likely optical counterpart of GRB 260310A (Konno et al., GCN 43974; Hamburg & Meegan,GCN 43975). Observations were carried out on 2026-03-14.80913 UT with the 0.30-m f/4 telescope at ABObservatory in clear band The obtained photometry is: 2026-03-14.80913 UT JD 2461114.30913 m_CV = 18.50 +/- 0.04 mag The measurement was calibrated against two APASS catalog stars,selected using Aladin. The reported magnitude is in the CV system. This measurement confirms that the optical counterpart is still clearly detected about 4.6 days after the GRB trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/44021. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42141] GRB 260310A / AT 2026fgk: iTelescope optical observations
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44020 SUBJECT: GRB 260310A / AT 2026fgk: iTelescope optical observations DATE: 26/03/15 15:06:06 GMT FROM: Filipp Dmitrievich Romanov at Amateur astronomer <filipp.romanov.27.04.1997(a)gmail.com> I observed the field of GRB 260310A = AT 2026fgk (Fermi GBM Team, GCN Circ. #43951) remotely using iTelescope.Net T21 (0.43-m f/6.8 reflector + CCD + f/4.5 focal reducer) in Utah Desert Remote Observatory at Great Basin Desert, Beryl Junction, Utah, USA. Six images with exposures of 300 sec. and Rc filter were obtained on 2026-03-15 from 08:56:17 UT (5.166 d. after the trigger) to 09:32:41 UT (5.191 d. after the trigger). I detected the optical afterglow and measured its magnitude (compared to Rc magnitudes of nearby stars from the ATLAS star catalog: Tonry et al., 2018) in the stacked image = 18.0 +/- 0.1 Rc. Magnitude is not corrected for Galactic extinction. The magnitude may be affected by contamination from the host galaxy. Stacked image: https://www.flickr.com/photos/filipp-romanov/55149149955/ F. D. Romanov (AAVSO). View this GCN Circular online at https://gcn.nasa.gov/circulars/44020. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42140] EP260314a: COLIBRÍ optical upper limit
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44019 SUBJECT: EP260314a: COLIBRÍ optical upper limit DATE: 26/03/15 12:33:39 GMT FROM: F. Fortin at IRAP <ffortin.sci.edu(a)gmail.com> Francis Fortin (IRAP), Edilberto Aguilar-Ruiz (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Missimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of EP260314a (Zhao et al., GCN Circ. 44010, Wu et al., GCN Circ. 44016) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-15 04:49:56 to 11:14:09 UTC (from 9.1 to 12.4 hours after the trigger) and obtained 144 minutes of simultaneous exposure in the i and z filters. The data were reduced and coadded with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect the SVOM/VT optical counterpart candidate reported by Li et al., GCN Circ. 44013 down to the following 3-sigma limit: i > 24.08 z > 23.17 While a direct comparison of magnitudes between the i, z filters and the VT filters is not possible, we suggest that our limits may be consistent with a fading of the VT optical candidate, which would strengthen the hypothesis that it is the true counterpart of EP260314A. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/44019. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42139] GRID detection of GRB 260312B
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44018 SUBJECT: GRID detection of GRB 260312B DATE: 26/03/15 11:40:03 GMT FROM: GRID Student Team at Tsinghua University <grid(a)tsinghua.edu.cn> Fanqing Zhou, Longhao Li, Chenyu Wang report on behalf of the GRID Collaboration: GRID-11B reports the detection of the long-duration GRB 260312B, which was also detected by Fermi GBM (GCN Circular 43969), MASTER-Kislovodsk (GCN Circular 43973), BALROG (GCN Circular 43970), Glowbug (GCN Circular 43976), AstroSat CZTI (GCN Circular 43989). The event was triggered with GRID on 2026-03-12 at 09:46:46 UTC. The measured burst duration (T90) in the 30-2000 keV range is approximately 11.8+/-2.3 seconds. The GRID light curve of this event can be found at https://mirrors.tuna.tsinghua.edu.cn/GRID/data/GRID-GCN/GRB260312B/GRID_260…. GRID is a student-led project to monitor the transient gamma-ray sky with multiple detectors onboard different nanosatellites in the era of multi-messenger astronomy. For more information about GRID, please refer to the following references: https://doi.org/10.1007/s10686-019-09636-w and https://doi.org/10.1007/s10686-021-09819-4. View this GCN Circular online at https://gcn.nasa.gov/circulars/44018. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42138] IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44017 SUBJECT: IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 26/03/15 11:21:27 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 26-03-15 at 02:19:06.60 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 3.3512 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/142272_46886533.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 26-03-15 Time: 02:19:06.60 UT RA: 175.69 (+0.49/-0.46 deg 90% PSF containment) J2000 Dec: -1.90 (+0.53/-0.51 deg 90% PSF containment) J2000 As announced in GCN Circular 43419 (https://gcn.nasa.gov/circulars/43419) IceCube alert notices for high-energy track alerts are now also streamed via Kafka. IceCube Gold/Bronze track alerts are available on the Kafka topic 'gcn.notices.icecube.gold_bronze_track_alerts'. The probability distribution of the true neutrino direction, allowing the extraction of precise 90% containment regions around the best-fit direction, is now available for revised reconstruction of high-energy track alerts. The corresponding sky map is distributed as a FITS file and follows the explicit naming convention IceCube-YYMMDDX, where YYMMDD indicates the date of the event and X is a letter distinguishing multiple alerts on the same day. The download link is provided through the GCN schema distributed via Kafka. Detailed documentation describing the alert distribution, schemas, and probability maps is available at: https://gcn.nasa.gov/missions/icecube. No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of this 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/44017. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42137] EP260314a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44016 SUBJECT: EP260314a: refined analysis of the EP-WXT and EP-FXT observations DATE: 26/03/15 09:29:55 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Yue Wu (NJU), Rui-Zhi Li (YNAO, CAS), Yaqi Zhao (USTC, PRIC) and Hai-Wu Pan (NAOC) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260314a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Zhao et al., GCN 44010). The transient was detected immediately when WXT observation started at T0=2026-03-14T22:51:20. The WXT observation lasted for approximately 16 seconds, and was interrupted due to the autonomous follow-up observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a hydrogen column density of 0.54（-0.27/+0.32）×10^22 cm^-2 and a photon index of 1.81(-0.75/+0.83). The derived average unabsorbed 0.5-4 keV flux is 2.14 (-0.55/+1.13) × 10^(-8) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously at 2026-03-14T22:54:51 (UTC, T0+211 s). The exposure time of this observation is 2.9ks. On-ground analysis of the FXT data found an uncatalogued source at R.A., Dec. = 211.8426, -23.4577 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the WXT position. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 0.22 (-0.07/+0.07) × 10^22 cm^-2 and a photon index of 2.21 (-0.27/+0.28). The derived average unabsorbed 0.5-10 keV flux is 5.11 (+0.46/-0.41) × 10^(-12) erg/s/cm^2. A follow-up observation with the EP/FXT was planned, and further information will be updated when the telemetry data is received. The optical follow-up observations were performed by Li et al. (GCN 44009), Li et al. (GCN 44013), Lipunov et al. (GCN 44014) and Pérez-García et al. (GCN 44015). We note that the SVOM/VT candidate (Li et al., GCN 44013) is located within the 10 arcsec error circle of EP/FXT. Further multi-band follow-up observations are encouraged to explore the nature of EP260314a. 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/44016. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42136] EP260314a: BOOTES-6/DPR optical upper limits at early times
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44015 SUBJECT: EP260314a: BOOTES-6/DPR optical upper limits at early times DATE: 26/03/15 09:27:12 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> I. Pérez-García, E. Fernández-García, M.D. Caballero-García, M. Gritsevich, S. Guziy, R. Sánchez-Ramírez, S.-Y. Wu, and A. J. Castro-Tirado (IAA-CSIC, Granada), P. J. Meintjes and H. J. van Heerden (UFS, South Africa), A. Martín-Carrillo and L. Hanlon (UCD, Ireland), Y.-D. Hu (GXU), D. R. Xiong (Yunnan Observatories of CAS) and C. J. Pérez del Pulgar (UMA, Malaga), on behalf of a larger collaboration, report: Following the detection of EP260314a by Einstein Probe (Zhao et al., GCNC 44010), the BOOTES-6/DPRT 0.6m robotic telescope at Boyden Observatory in Maselspoort (South Africa) responded to this event starting on Mar 14, 23:00:01 UT (~ 8.5 min after trigger) with a 10s clear filter image. No new source is detected at the position of the proposed optical counterpart by SVOM/VT (Li et al., GCNC 44013) up to magnitude 16.3 using Gaia DR3 Gmag magnitude as reference on our first image. Further images were gathered and using ATLAS REFCAT2 as reference (Tonry et al. 2018) we get upper limits of: 18.5 (60s clear, at 23:03 UT), 20.9 (300s clear, at 23:06 UT) and 21.7 (600s clear, at 23:18 UT), in agreement with the upper limit reported by LCO (Li et al. GCNC 44009). We thank the staff at Boyden Observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/44015. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42135] EP260314a: Global MASTER-Net observations report
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44014 SUBJECT: EP260314a: Global MASTER-Net observations report DATE: 26/03/15 09:18:43 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 [1] located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP260314a ( EP Team et al., GCN 44010) errorbox 18771 sec after notice time and 31448 sec after trigger time at 2026-03-15 07:35:44 UT, with upper limit up to 20.4 mag. The observations began at zenith distance = 10 deg. The sun altitude is -37.3 deg. The galactic latitude b = 36 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=3187114 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 31478 | 2026-03-15 07:35:44 | MASTER-OAFA | (14h 03m 09.70s , -23d 05m 06.7s) | C | 60 | 20.1 | 31538 | 2026-03-15 07:35:44 | MASTER-OAFA | (14h 03m 09.70s , -23d 05m 06.8s) | C | 180 | 20.4 | Coadd 31555 | 2026-03-15 07:37:01 | MASTER-OAFA | (14h 11m 52.28s , -23d 06m 44.8s) | C | 60 | 20.0 | 31615 | 2026-03-15 07:37:01 | MASTER-OAFA | (14h 11m 52.28s , -23d 06m 44.8s) | C | 180 | 20.4 | Coadd 31632 | 2026-03-15 07:38:17 | MASTER-OAFA | (14h 03m 12.03s , -23d 05m 00.4s) | C | 60 | 20.0 | 31707 | 2026-03-15 07:39:33 | MASTER-OAFA | (14h 11m 49.57s , -23d 06m 01.9s) | C | 60 | 20.0 | 31784 | 2026-03-15 07:40:49 | MASTER-OAFA | (14h 03m 07.51s , -23d 04m 36.7s) | C | 60 | 20.0 | 33575 | 2026-03-15 08:10:40 | MASTER-OAFA | (14h 11m 51.09s , -23d 04m 19.3s) | C | 60 | 20.0 | 33650 | 2026-03-15 08:11:56 | MASTER-OAFA | (14h 11m 57.93s , -23d 05m 18.8s) | C | 60 | 19.9 | 33710 | 2026-03-15 08:11:56 | MASTER-OAFA | (14h 11m 57.94s , -23d 05m 18.8s) | C | 180 | 20.4 | Coadd 33726 | 2026-03-15 08:13:11 | MASTER-OAFA | (14h 11m 51.16s , -23d 06m 17.7s) | C | 60 | 19.8 | 33806 | 2026-03-15 08:14:32 | MASTER-OAFA | (14h 03m 15.81s , -23d 05m 54.0s) | C | 60 | 20.0 | 33866 | 2026-03-15 08:14:32 | MASTER-OAFA | (14h 03m 15.81s , -23d 05m 54.1s) | C | 180 | 20.4 | Coadd 33886 | 2026-03-15 08:15:52 | MASTER-OAFA | (14h 03m 12.24s , -23d 04m 20.5s) | C | 60 | 20.1 | 33966 | 2026-03-15 08:17:12 | MASTER-OAFA | (14h 03m 12.30s , -23d 05m 42.2s) | C | 60 | 20.1 | 35185 | 2026-03-15 08:36:30 | MASTER- | (14h 07m 08.18s , -23d 27m 00.1s) | C | 180 | 19.3 | 35185 | 2026-03-15 08:36:30 | MASTER- | (14h 08m 27.19s , -24d 01m 06.3s) | C | 180 | 19.5 | 35377 | 2026-03-15 08:39:42 | MASTER- | (14h 07m 13.49s , -23d 28m 05.1s) | C | 180 | 19.6 | 35377 | 2026-03-15 08:39:42 | MASTER- | (14h 08m 32.57s , -24d 02m 10.3s) | C | 180 | 19.6 | 35568 | 2026-03-15 08:42:54 | MASTER- | (14h 07m 08.52s , -23d 29m 07.4s) | C | 180 | 19.5 | 35568 | 2026-03-15 08:42:54 | MASTER- | (14h 08m 27.64s , -24d 03m 12.2s) | C | 180 | 19.8 | 35534 | 2026-03-15 08:43:20 | MASTER-OAFA | (14h 11m 56.24s , -23d 04m 00.8s) | C | 60 | 19.9 | 35610 | 2026-03-15 08:44:36 | MASTER-OAFA | (14h 11m 56.27s , -23d 05m 30.6s) | C | 60 | 19.9 | 35760 | 2026-03-15 08:46:05 | MASTER- | (14h 07m 13.91s , -23d 28m 54.9s) | C | 180 | 19.3 | 35760 | 2026-03-15 08:46:05 | MASTER- | (14h 08m 33.15s , -24d 02m 59.4s) | C | 180 | 19.8 | 35891 | 2026-03-15 08:49:17 | MASTER-OAFA | (14h 03m 17.80s , -23d 04m 26.7s) | C | 60 | 20.0 | 35951 | 2026-03-15 08:49:17 | MASTER- | (14h 07m 10.42s , -23d 27m 22.5s) | C | 180 | 19.4 | 35951 | 2026-03-15 08:49:17 | MASTER- | (14h 08m 29.74s , -24d 01m 26.6s) | C | 180 | 19.9 | 36142 | 2026-03-15 08:52:28 | MASTER- | (14h 07m 10.07s , -23d 29m 05.4s) | C | 180 | 19.6 | 36142 | 2026-03-15 08:52:28 | MASTER- | (14h 08m 29.52s , -24d 03m 08.8s) | C | 180 | 19.8 | 36335 | 2026-03-15 08:55:40 | MASTER- | (14h 07m 12.33s , -23d 27m 15.8s) | C | 180 | 19.7 | 36335 | 2026-03-15 08:55:40 | MASTER- | (14h 08m 31.87s , -24d 01m 18.8s) | C | 180 | 19.9 | 36526 | 2026-03-15 08:58:52 | MASTER- | (14h 07m 05.49s , -23d 28m 09.4s) | C | 180 | 19.8 | 36526 | 2026-03-15 08:58:52 | MASTER- | (14h 08m 25.17s , -24d 02m 11.9s) | C | 180 | 19.8 | 36723 | 2026-03-15 09:02:09 | MASTER- | (14h 07m 05.49s , -23d 27m 09.1s) | C | 180 | 19.8 | 36723 | 2026-03-15 09:02:09 | MASTER- | (14h 08m 25.25s , -24d 01m 11.3s) | C | 180 | 19.8 | 36914 | 2026-03-15 09:05:20 | MASTER- | (14h 07m 12.73s , -23d 28m 09.7s) | C | 180 | 19.7 | 36914 | 2026-03-15 09:05:20 | MASTER- | (14h 08m 32.56s , -24d 02m 11.3s) | C | 180 | 19.8 | 37105 | 2026-03-15 09:08:31 | MASTER- | (14h 07m 05.16s , -23d 29m 09.4s) | C | 180 | 19.7 | 37105 | 2026-03-15 09:08:31 | MASTER- | (14h 08m 25.09s , -24d 03m 10.6s) | C | 180 | 19.6 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44014. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42134] EP260314a: SVOM/VT optical candidate
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44013 SUBJECT: EP260314a: SVOM/VT optical candidate DATE: 26/03/15 03:58:26 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, Y. N. Ma, C. Wu, Z. H. Yao, Y. L. Qiu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. T. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observation of the field of EP260314a detected by Einstein Probe (Zhao et al., GCN 44010). The observation started at 2026-03-14T23:03:04 UTC, i.e., about 11.5 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. An uncatalogued optical source was detected in VT_R stacked image within the error box of FXT (Zhao et al., GCN 44010). The position is at R.A., Dec. = 211.842259, -23.457728 degrees, equivalent to: R.A. (J2000) = +14:07:22.14 Dec. (J2000) = -23:27:27.82 with an uncertainty of 0.5 arcsec. The measurements in AB magnitudes are given below: Mid_time Band Exposure Time Magnitude (AB) 1.07 hour VT_R 29*50 sec 22.70+/-0.26 mag 1.07 hour VT_B 29*50 sec > 23.0 mag With the available data, we could not confirm the fading of the candidate. Our photometry was not corrected for Galactic extinction. 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/44013. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42133] Fermi trigger No 795185313: Global MASTER-Net observations report
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44012 SUBJECT: Fermi trigger No 795185313: Global MASTER-Net observations report DATE: 26/03/15 03:30:44 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 [1] located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB260314.53 (trigger No 795185313,14h 23m 00.00s , -11d 19m 58.8s, R=50) errorbox 48826 sec after notice time and 48862 sec after trigger time at 2026-03-15 02:22:50 UT, with upper limit up to 20.4 mag. The observations began at zenith distance = 45 deg. The sun altitude is -42.8 deg. The galactic latitude b = 45 deg., longitude l = 337 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3186061 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 48883 | 2026-03-15 02:22:50 | MASTER-OAFA | (11h 42m 55.30s , -01d 47m 48.0s) | C | 40 | 19.7 | 48943 | 2026-03-15 02:22:50 | MASTER-OAFA | (11h 42m 55.30s , -01d 47m 48.0s) | C | 160 | 20.4 | Coadd 48934 | 2026-03-15 02:23:36 | MASTER-OAFA | (11h 42m 55.23s , -01d 47m 46.9s) | C | 50 | 19.8 | 48999 | 2026-03-15 02:24:32 | MASTER-OAFA | (11h 42m 55.19s , -01d 47m 45.7s) | C | 70 | 19.9 | 49081 | 2026-03-15 02:25:48 | MASTER-OAFA | (11h 42m 55.10s , -01d 47m 45.0s) | C | 80 | 19.9 | 49191 | 2026-03-15 02:25:48 | MASTER-OAFA | (11h 42m 55.10s , -01d 47m 45.0s) | C | 300 | 20.0 | Coadd 49177 | 2026-03-15 02:27:15 | MASTER-OAFA | (11h 42m 54.96s , -01d 47m 43.8s) | C | 100 | 20.0 | 49293 | 2026-03-15 02:29:01 | MASTER-OAFA | (11h 42m 54.80s , -01d 47m 42.7s) | C | 120 | 20.1 | 49429 | 2026-03-15 02:31:07 | MASTER-OAFA | (11h 42m 54.61s , -01d 47m 41.6s) | C | 140 | 20.2 | 49544 | 2026-03-15 02:31:07 | MASTER-OAFA | (11h 42m 54.61s , -01d 47m 41.6s) | C | 370 | 20.0 | Coadd 49590 | 2026-03-15 02:33:33 | MASTER-OAFA | (11h 42m 54.38s , -01d 47m 40.7s) | C | 170 | 20.3 | 49711 | 2026-03-15 02:36:29 | MASTER-OAFA | (11h 42m 54.21s , -01d 47m 40.3s) | C | 60 | 19.8 | 49777 | 2026-03-15 02:37:35 | MASTER-OAFA | (11h 42m 54.10s , -01d 47m 40.2s) | C | 60 | 19.9 | 49837 | 2026-03-15 02:37:35 | MASTER-OAFA | (11h 42m 54.10s , -01d 47m 40.1s) | C | 180 | 20.4 | Coadd 49843 | 2026-03-15 02:38:40 | MASTER-OAFA | (11h 42m 54.00s , -01d 47m 39.9s) | C | 60 | 19.9 | 49909 | 2026-03-15 02:39:47 | MASTER-OAFA | (11h 42m 53.89s , -01d 47m 39.7s) | C | 60 | 19.9 | 49974 | 2026-03-15 02:40:52 | MASTER-OAFA | (11h 42m 53.81s , -01d 47m 39.7s) | C | 60 | 19.9 | 50034 | 2026-03-15 02:40:52 | MASTER-OAFA | (11h 42m 53.81s , -01d 47m 39.7s) | C | 180 | 20.4 | Coadd 50040 | 2026-03-15 02:41:57 | MASTER-OAFA | (11h 42m 53.70s , -01d 47m 39.5s) | C | 60 | 19.8 | 50106 | 2026-03-15 02:43:04 | MASTER-OAFA | (11h 42m 53.59s , -01d 47m 39.7s) | C | 60 | 19.9 | 50172 | 2026-03-15 02:44:10 | MASTER-OAFA | (11h 42m 53.49s , -01d 47m 39.9s) | C | 60 | 19.9 | 50232 | 2026-03-15 02:44:10 | MASTER-OAFA | (11h 42m 53.49s , -01d 47m 39.9s) | C | 180 | 20.4 | Coadd 50237 | 2026-03-15 02:45:15 | MASTER-OAFA | (11h 42m 53.37s , -01d 47m 40.1s) | C | 60 | 19.9 | 50304 | 2026-03-15 02:46:21 | MASTER-OAFA | (11h 42m 53.26s , -01d 47m 40.2s) | C | 60 | 19.8 | 50369 | 2026-03-15 02:47:27 | MASTER-OAFA | (11h 42m 53.14s , -01d 47m 40.1s) | C | 60 | 19.9 | 50429 | 2026-03-15 02:47:27 | MASTER-OAFA | (11h 42m 53.14s , -01d 47m 40.1s) | C | 180 | 20.0 | Coadd 50434 | 2026-03-15 02:48:32 | MASTER-OAFA | (11h 42m 53.02s , -01d 47m 40.5s) | C | 60 | 19.9 | 50500 | 2026-03-15 02:49:38 | MASTER-OAFA | (11h 42m 52.89s , -01d 47m 40.4s) | C | 60 | 19.9 | 50566 | 2026-03-15 02:50:44 | MASTER-OAFA | (11h 42m 52.77s , -01d 47m 40.4s) | C | 60 | 19.9 | 50626 | 2026-03-15 02:50:44 | MASTER-OAFA | (11h 42m 52.77s , -01d 47m 40.4s) | C | 180 | 20.4 | Coadd 50632 | 2026-03-15 02:51:49 | MASTER-OAFA | (11h 42m 52.64s , -01d 47m 40.6s) | C | 60 | 19.9 | 50698 | 2026-03-15 02:52:56 | MASTER-OAFA | (11h 42m 52.47s , -01d 47m 40.8s) | C | 60 | 19.9 | 50764 | 2026-03-15 02:54:02 | MASTER-OAFA | (11h 42m 52.36s , -01d 47m 41.4s) | C | 60 | 19.9 | 50824 | 2026-03-15 02:54:02 | MASTER-OAFA | (11h 42m 52.36s , -01d 47m 41.4s) | C | 180 | 20.0 | Coadd 50829 | 2026-03-15 02:55:07 | MASTER-OAFA | (11h 42m 52.22s , -01d 47m 41.7s) | C | 60 | 19.9 | 50896 | 2026-03-15 02:56:13 | MASTER-OAFA | (11h 42m 52.09s , -01d 47m 42.1s) | C | 60 | 19.9 | 50961 | 2026-03-15 02:57:19 | MASTER-OAFA | (11h 42m 51.92s , -01d 47m 42.9s) | C | 60 | 19.9 | 51021 | 2026-03-15 02:57:19 | MASTER-OAFA | (11h 42m 51.92s , -01d 47m 42.9s) | C | 180 | 20.0 | Coadd 51027 | 2026-03-15 02:58:24 | MASTER-OAFA | (11h 42m 51.79s , -01d 47m 43.3s) | C | 60 | 19.9 | 51093 | 2026-03-15 02:59:31 | MASTER-OAFA | (11h 42m 51.62s , -01d 47m 43.7s) | C | 60 | 19.9 | 51159 | 2026-03-15 03:00:36 | MASTER-OAFA | (11h 42m 51.50s , -01d 47m 44.1s) | C | 60 | 19.9 | 51219 | 2026-03-15 03:00:36 | MASTER-OAFA | (11h 42m 51.50s , -01d 47m 44.0s) | C | 180 | 20.0 | Coadd 51224 | 2026-03-15 03:01:42 | MASTER-OAFA | (11h 42m 51.36s , -01d 47m 44.9s) | C | 60 | 19.9 | 51291 | 2026-03-15 03:02:48 | MASTER-OAFA | (11h 42m 51.20s , -01d 47m 45.9s) | C | 60 | 19.9 | 51356 | 2026-03-15 03:03:54 | MASTER-OAFA | (11h 42m 51.07s , -01d 47m 46.3s) | C | 60 | 19.9 | 51416 | 2026-03-15 03:03:54 | MASTER-OAFA | (11h 42m 51.07s , -01d 47m 46.3s) | C | 180 | 20.0 | Coadd 51421 | 2026-03-15 03:04:59 | MASTER-OAFA | (11h 42m 50.89s , -01d 47m 46.6s) | C | 60 | 20.0 | 51488 | 2026-03-15 03:06:06 | MASTER-OAFA | (11h 42m 50.76s , -01d 47m 47.3s) | C | 60 | 19.9 | 51553 | 2026-03-15 03:07:11 | MASTER-OAFA | (11h 42m 50.58s , -01d 47m 48.2s) | C | 60 | 19.9 | 51613 | 2026-03-15 03:07:11 | MASTER-OAFA | (11h 42m 50.58s , -01d 47m 48.2s) | C | 180 | 20.0 | Coadd 51619 | 2026-03-15 03:08:17 | MASTER-OAFA | (11h 42m 50.44s , -01d 47m 49.1s) | C | 60 | 19.9 | 51686 | 2026-03-15 03:09:24 | MASTER-OAFA | (11h 42m 50.31s , -01d 47m 49.8s) | C | 60 | 19.9 | 51751 | 2026-03-15 03:10:29 | MASTER-OAFA | (11h 42m 50.15s , -01d 47m 50.8s) | C | 60 | 19.9 | 51811 | 2026-03-15 03:10:29 | MASTER-OAFA | (11h 42m 50.15s , -01d 47m 50.8s) | C | 180 | 20.0 | Coadd 51816 | 2026-03-15 03:11:34 | MASTER-OAFA | (11h 42m 50.01s , -01d 47m 51.7s) | C | 60 | 19.9 | 51883 | 2026-03-15 03:12:40 | MASTER-OAFA | (11h 42m 49.85s , -01d 47m 53.2s) | C | 60 | 19.9 | 51948 | 2026-03-15 03:13:46 | MASTER-OAFA | (11h 42m 49.69s , -01d 47m 53.9s) | C | 60 | 19.9 | 52008 | 2026-03-15 03:13:46 | MASTER-OAFA | (11h 42m 49.69s , -01d 47m 53.9s) | C | 180 | 20.0 | Coadd 52014 | 2026-03-15 03:14:51 | MASTER-OAFA | (11h 42m 49.52s , -01d 47m 54.8s) | C | 60 | 19.9 | 52080 | 2026-03-15 03:15:58 | MASTER-OAFA | (11h 42m 49.36s , -01d 47m 55.6s) | C | 60 | 19.9 | 52146 | 2026-03-15 03:17:03 | MASTER-OAFA | (11h 42m 49.19s , -01d 47m 56.2s) | C | 60 | 19.9 | 52206 | 2026-03-15 03:17:03 | MASTER-OAFA | (11h 42m 49.19s , -01d 47m 56.2s) | C | 180 | 20.0 | Coadd 52211 | 2026-03-15 03:18:09 | MASTER-OAFA | (11h 42m 49.02s , -01d 47m 57.7s) | C | 60 | 19.9 | 52277 | 2026-03-15 03:19:14 | MASTER-OAFA | (11h 42m 48.86s , -01d 47m 58.8s) | C | 60 | 19.9 | 52342 | 2026-03-15 03:20:20 | MASTER-OAFA | (11h 42m 48.71s , -01d 48m 00.4s) | C | 60 | 19.9 | 52408 | 2026-03-15 03:21:26 | MASTER-OAFA | (11h 42m 48.52s , -01d 48m 01.7s) | C | 60 | 19.9 | 52474 | 2026-03-15 03:22:32 | MASTER-OAFA | (11h 42m 48.36s , -01d 48m 02.8s) | C | 60 | 19.9 | 52540 | 2026-03-15 03:23:37 | MASTER-OAFA | (11h 42m 48.20s , -01d 48m 04.0s) | C | 60 | 19.9 | 52605 | 2026-03-15 03:24:43 | MASTER-OAFA | (11h 42m 48.01s , -01d 48m 05.0s) | C | 60 | 19.9 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44012. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42132] IceCube Alert 260315A: Global MASTER-Net observations report
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44011 SUBJECT: IceCube Alert 260315A: Global MASTER-Net observations report DATE: 26/03/15 02:40:16 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 [1] located in Argentina (OAFA observatory of San Juan National University) was pointed to the IceCube Alert 260315A (trigger No 46886533,11h 42m 40.32s , -01d 53m 06.0s, R=0.71) errorbox 105 sec after notice time and 224 sec after trigger time at 2026-03-15 02:22:50 UT, with upper limit up to 20.4 mag. The observations began at zenith distance = 45 deg. The sun altitude is -42.8 deg. The galactic latitude b = 57 deg., longitude l = 272 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3187113 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 244 | 2026-03-15 02:22:50 | MASTER-OAFA | (11h 42m 55.30s , -01d 47m 48.0s) | C | 40 | 19.7 | 304 | 2026-03-15 02:22:50 | MASTER-OAFA | (11h 42m 55.30s , -01d 47m 48.0s) | C | 160 | 20.4 | Coadd 295 | 2026-03-15 02:23:36 | MASTER-OAFA | (11h 42m 55.23s , -01d 47m 46.9s) | C | 50 | 19.8 | 361 | 2026-03-15 02:24:32 | MASTER-OAFA | (11h 42m 55.19s , -01d 47m 45.7s) | C | 70 | 19.9 | 442 | 2026-03-15 02:25:48 | MASTER-OAFA | (11h 42m 55.10s , -01d 47m 45.0s) | C | 80 | 19.9 | 552 | 2026-03-15 02:25:48 | MASTER-OAFA | (11h 42m 55.10s , -01d 47m 45.0s) | C | 300 | 20.0 | Coadd 539 | 2026-03-15 02:27:15 | MASTER-OAFA | (11h 42m 54.96s , -01d 47m 43.8s) | C | 100 | 20.0 | 655 | 2026-03-15 02:29:01 | MASTER-OAFA | (11h 42m 54.80s , -01d 47m 42.7s) | C | 120 | 20.1 | 790 | 2026-03-15 02:31:07 | MASTER-OAFA | (11h 42m 54.61s , -01d 47m 41.6s) | C | 140 | 20.2 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44011. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42131] EP260314a: Einstein Probe detection of an X-ray transient
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44010 SUBJECT: EP260314a: Einstein Probe detection of an X-ray transient DATE: 26/03/15 02:16:51 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Yaqi Zhao (USTC, PRIC), Yue Wu (NJU), Rui-Zhi Li (YNAO, CAS) and Hai-Wu Pan (NAOC) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260314a. The transient triggered EP-WXT (ID: 01709258851) at 2026-03-14T22:51:36 (UTC). The WXT position of the source is R.A. = 211.845 deg, DEC = -23.445 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 211.8437 deg, DEC = -23.4601 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. 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/44010. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42130] The EP-WXT trigger 01709258851: Las Cumbres upper limit
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44009 SUBJECT: The EP-WXT trigger 01709258851: Las Cumbres upper limit DATE: 26/03/15 01:07:35 GMT FROM: Wenxiong Li at NAOC <liwenxiong1992(a)gmail.com> Wenxiong Li, Runduo Liang (NAOC), Iair Arcavi, Ido Keinan (TAU), David Sand (U of Arizona) We observed the position of the EP-WXT trigger 01709258851 with a Las Cumbres 1m telescope at Sutherland Observatory, South Africa, 50 mins after the Einstein Probe WXT trigger. We took 4x300s exposures in the broad optical w band. We didn’t detect any uncataloged source within the EP-WXT error circle down to a limiting r-band mag of 21.5 mag. View this GCN Circular online at https://gcn.nasa.gov/circulars/44009. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42129] GRB 260314A: GECAM-B observation of a burst
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44008 SUBJECT: GRB 260314A: GECAM-B observation of a burst DATE: 26/03/15 01:04:49 GMT FROM: xueyuan zao <zaoxueyuan(a)gmail.com> Xue-Yuan Zao, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 260314A, at 2026-03-14T00:58:53.100 UTC, which is also detected by Fermi/GBM (Fermi GBM team, GCN #43997). The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260314A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/44008. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42128] Fermi Gamma-ray Burst Monitor trigger 795185313/260314534 is not a GRB
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44007 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 795185313/260314534 is not a GRB DATE: 26/03/14 18:19:35 GMT FROM: Bagrat Mailyan at Florida Tech <mbagrat(a)gmail.com> B. Mailyan (Florida Tech) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 795185313/260314534 at 12:48:28.23 UT on 14 March 2026, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely accidental." View this GCN Circular online at https://gcn.nasa.gov/circulars/44007. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42127] GRB 260310A / AT2026fgk: SAO RAS optical observations
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44006 SUBJECT: GRB 260310A / AT2026fgk: SAO RAS optical observations DATE: 26/03/14 15:46:52 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), O. Spiridonova (SAO RAS), A. Pozanenko (IKI), N. Pankov (IKI), A. Volnova (IKI), report on behalf of GRB follow-up team and IKI-GRB-FuN. We observed the field of the AT2026fgk, potential counterpart of the GRB 260310A (Fermi GBM team, GCN 43951; Hamburg and Meegan, GCN 43975; Salunke et al., GCN 43958) with the Zeiss-1000 1m telescope of the SAO RAS equipped with the CCD photometer. We obtained series of 300 sec images in B, V, Rc, Ic filters on March 12/13 and 13/14. The observations carried out under a good weather conditions and typical seeing of 1".5--2".5. The candidate discovered by GOTO (O'Neill et al. 2026, TNS Discovery Report 294132) and observed by numerous observatories (Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979; Moren Méndez et al., GCN 43980; de Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Pursiainen et al., GCN 43990; Becerra et al., GCN 43991; Li et al., GCN 43993; Jayaraman et al., GCN 43994; Stein et al., GCN 43996; Martin-Carrillo et al., GCN 44000; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo, GCN 44003; Brivio et al., GCN 44004; Rhodes et al., GCN 44005) is clearly detected in our images with the following brightness. Date UT_start t_mid - T0, filter exp, mag +/- err days s 2026.03.12T23:27:00 2.80565 B 5*300 18.77 +/- 0.01 2026.03.12T23:09:50 2.79577 Rc 6*300 18.00 +/- 0.01 2026.03.13T23:56:42 3.82450 B 5*300 18.92 +/- 0.01 2026.03.13T23:45:30 3.81664 Rc 4*300 18.14 +/- 0.01 This preliminary photometry is based on the nearby stars from PanSTARRS catalogue. Magnitudes of standards converted to B, Rc with the Lupton 2005 equations. The magnitudes of the AT2026fgk are not corrected for Galactic and host extinction and may be contaminated by the host galaxy. We can not trace any colour evolution between the two epochs (2.8 and 3.8 days after GRB trigger). View this GCN Circular online at https://gcn.nasa.gov/circulars/44006. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42126] GRB 260310A/AT 2026fgk: radio detection at 15GHz
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44005 SUBJECT: GRB 260310A/AT 2026fgk: radio detection at 15GHz DATE: 26/03/14 15:23:56 GMT FROM: Lauren Rhodes at McGill <lauren.rhodes(a)mcgill.ca> Lauren Rhodes (McGill), Andrew Hughes, Rob Fender (Oxford), Joe Bright (Oxford/Breakthrough Listen), Dave Green, Dave Titterington (Cambridge) report: We observed the position of GRB 260310A/AT 2026fgk (Fermi GBM Team, GCN 43951; Konno et al., GCN 43974; Hinds et al., AstroNote 2026-65; O’Neill et al. 2026, TNS Discovery Report 294132) with the Arcminute Microkelvin Imager Large-Array (AMI-LA) at 15.2 GHz beginning at 2026 March 13 23:20:06 for a total of 8 hours. The flux standard 3c286 was used to calibrate the bandpass response and flux scale of the AMI-LA and J1435+7605 was used as an interleaved complex gain calibrator. We detect an unresolved source with coordinates consistent with those of GRB 260310A/AT 2026fgk. We measure a peak flux density of 9.8 +/- 0.5 mJy/beam. Given the high flux density of the source, we cross checked with the VLASS survey and find no preexisting radio emission at the afterglow coordinates down to a 3sigma upper limit of around 0.5mJy/beam. We thank the staff at the Mullard Radio Astronomy Observatory for carrying out these observations and operating the AMI-LA. View this GCN Circular online at https://gcn.nasa.gov/circulars/44005. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42125] GRB 260310A / AT2026fgk: TNG NIR detection
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44004 SUBJECT: GRB 260310A / AT2026fgk: TNG NIR detection DATE: 26/03/14 14:48:10 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio (INAF-OAB), D. Malesani (DAWN/NBI and Radboud), L. Izzo (INAF-OACn and DARK/NBI), P. D’Avanzo (INAF-OAB), V. D’Elia (ASI-SSDC), A. Melandri (INAF-OAR), A. Rossi (INAF-OAS), M. de Pasquale (Univ. Messina), Aldo Fiorenzano (INAF-TNG), Carmen Padilla (INAF-TNG) report on behalf of the CIBO collaboration: We observed the likely counterpart of GRB 260310A, detected by Fermi/GBM (Fermi GBM team, GCN 43951; Hamburg & Meagan, GCNC 43975) and AstroSat CZTI (Salunke et al., GCN 43958) with the Italian 3.6m TNG telescope equipped with the near-infrared camera NICS. A series of images was obtained with the J and H filters starting on 2026 March 14 at 05:11:46 UT (i.e. 96.2 hours after the burst), and lasted 40 minutes for each filter. The optical/NIR counterpart, also reported as AT2026fgk (Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979; Moreno Méndez et al., GCN 43980; de Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Pursiainen et al., GCN 43990; Becerra et al., GCN 43991; Li et al., GCN 43993; Stein et al, GCN 43996; Martin-Carrillo et al., GCN 44000; Watson et al., GCN 44001; Lai et al., GCN 44002; L. Izzo, GCN 44003) is detected in the co-added images with the following magnitudes: J = 17.0 +/- 0.1 (Vega, calibrated against the 2MASS catalogue), at a mid-time of 96.5 hr after the trigger; H = 15.9 +/- 0.1 (Vega, calibrated against the 2MASS catalogue), at a mid-time of 97.1 hr after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/44004. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42124] GRB 260310A / AT2026fgk: OASDG optical observations
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44003 SUBJECT: GRB 260310A / AT2026fgk: OASDG optical observations DATE: 26/03/14 09:12:46 GMT FROM: luca.izzo(a)inaf.it L. Izzo (INAF-OACn and DARK/NBI) reports: We observed the likely counterpart of GRB 261013A (Fermi GBM team, GCN #43951; Hamburg et al., GCN #43975) using the 0.5-m T1 telescope of the Osservatorio Astronomico S. Di Giacomo, located in Agerola, Italy. Our observations started on 2026 March 14 at 00:04 UT, 3.797 days after the GRB trigger. We acquired a series of 8 × 300 s images in the Rc and Ic filters. The optical counterpart, also reported as AT2026fgk (Konno et al., GCN #43974; Hinds et al., GCN #43977; Lipunov et al., GCN #43978; Martin-Carrillo et al., GCN #43979; Moreno Méndez et al., GCN #43980; de Ugarte Postigo et al., GCN #43984; Hsu et al., GCN #43986; Pursiainen et al., GCN #43990; Becerra et al., GCN #43991; Martin-Carrillo et al., GCN #44000; Watson et al., GCN #44001; Lai et al., GCN #44002) is clearly detected in the individual frames. In the Rc-band stacked image, we measure a preliminary magnitude of Rc = 18.21 +/- 0.07 mag (AB), calibrated against nearby stars from the Pan-STARRS catalog and appropriately transformed to Rc magnitudes. The measured magnitude may still be affected by contamination from the bright host galaxy, but further analysis is ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/44003. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42123] GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44002 SUBJECT: GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations DATE: 26/03/14 08:19:29 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> C.-H. Lai, A. Aryan, Y.-H. Lee, C.-S. Lin, T.-W. Chen (all NCU), A. K. H. Kong (NTHU), J. H. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), A. Sankar.K, M.-H. Lee, Y.-C. Pan, C.-C. Ngeow, W.-J. Hou, H.-Y. Hsiao, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz, and M. Huber (both IfA, Hawaii) report: We performed multiband optical observations of the field of the GRB 260310A (Fermi GBM team, GCN 43951, Hamburg et al., GCN 43975) using the 1m LOT at the Lulin observatory, as part of the Kinder collaboration (Chen et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first LOT epoch of observations in g-band started at 13:45 UTC on 13th of March 2026 (MJD 61092.577), 3.37 days after the Fermi GBM detection. The reported optical counterpart, AT 2026fgk (Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979; Moreno Méndez et al., GCN 43980; Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Pursiainen et al., GCN 43990; Becerra et al., GCN 43991; Martin-Carrillo et al., GCN 44000; Watson et al., GCN 44001), is clearly visible in each individual frame. The GRB also had X-ray (Salunke et al., GCN 43958; Jayaraman et al., GCN 43994) and NIR (Li et al., GCN 43993; Stein et al., GCN 43996) detections. We utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtractions with the Pan-STARRS1 3Pi archive images (Chambers et al. 2016 arXiv:1612.05560) using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. Moreover, we further used AutoPhOT to perform PSF photometry. The details of the observations and the measured photometry (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (d) | Exposure (s) | Magnitude | avg.Seeing | Airmass LOT | g | 61112.573 | 3.367 | 300 * 1 | 18.72 +/- 0.02 | 1".94 | 2.35 LOT | r | 61112.576 | 3.371 | 300 * 1 | 18.42 +/- 0.02 | 1".70 | 2.32 LOT | i | 61112.581 | 3.374 | 300 * 1 | 18.26 +/- 0.02 | 1".77 | 2.28 LOT | z | 61112.584 | 3.378 | 300 * 1 | 17.96 +/- 0.05 | 1".90 | 2.25 In multiband photometry, the optical counterpart appears red. The presented magnitudes are calibrated using the field stars from the ATLAS-refcat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105). In the direction of the transient, these magnitudes are not corrected for the expected Galactic foreground extinctions of 0.09, 0.06, 0.04, and 0.03 mags (Schlafly & Finkbeiner 2011) for the g, r, i, and z bands, respectively. The details on the Lulin observatory telescopes and the follow-up methodology for such transients are presented in Aryan et al. (2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69). View this GCN Circular online at https://gcn.nasa.gov/circulars/44002. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42122] GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44001 SUBJECT: GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations DATE: 26/03/14 06:20:02 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Alan M. Watson (UNAM), Damien Dornic (CPPM), Rosa L. Becerra (UNAM), Antonio de Ugarte Postigo (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Camila Angulo (UNAM), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Benjamin Schneider (LAM) report: We again imaged the field of AT 2026fgk (Lipunov et al., GCN Circ. 43954; Konno et al., GCN Circ. 43975; Hinds et al., GCN Circ. 43977; Lipunov et al., GCN Circ. 43978, Martin-Carrillo et al., GCN Circ. 43079; Moren Méndez et al., GCN Circ 43980; de Ugarte Postiga et al., GCN Circ. 43984; Hsu et al., GCN Circ. 43986; Pursiainen et al., GCN Circ. 43990; Becerra et al., GCN Circ 43991; Li et al., GCn Circ. 43993; Stein et al., GCN Circ 43996; Martin-Carrillo et al., GCn Circ. 44000), a possible counterpart of the Fermi GBM GRB 260310A (Fermi GBM Team, GCN Circ. 43951; Humburg & Meegan, GCN Circ. 43975) and also detected by AstroSat CZTI (Salunke et al., GCN Circ. 43958), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-14 02:46 to 05:07 UTC (from 93.82 to 96.17 hours after the GRB trigger) and obtained 15, 14, and 28 minutes, respectively, of exposure in the g, r, and z filters. The data were reduced, coadded, calibrated, and analysed with the ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked images, we continue to detect AT 2026fgk with a preliminary PSF magnitude of: r = 18.47 +/- 0.01 Compared to the magnitudes in our first epoch reported in Moreno Méndez et al. (GCN Circ. 43980), we estimate a temporal decay index of about -1.2, consistent with the normal decay observed in GRBs. Moreover, from the optical/IR magnitudes from our first epoch and the photometry reported with WINTER (Stein et al., GCN Circ. 43996) between T+71.5 and T+72.5 hours, we estimate a spectral index beta of about -1.1 also supporting a synchrotron spectrum and a likely origin in a GRB afterglow. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/44001. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42121] GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44000 SUBJECT: GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay DATE: 26/03/14 04:43:17 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> A. Martin-Carrillo, E. Aasen, L. Brown, D. Colfer, M. Collins, J. Costello, C. Harris, R. Odunuga, H. O'Leary Jeffers, C. O'Malley, J. Parimkayala, J. Roca Garcia-Valino, R. Roddy, D. Scott, A. Valdivia y Alvarado Carvajal (UCD), A. Fernandez-Martin (CAHA), J. F. Agui Fernandez (CAHA), report on behalf of a larger collaboration: We observed the position of AT2026fgk, the likely counterpart to GRB 260310A (Fermi GBM team, GCN 43951; Salunke et al., GCN 43958; Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979; Méndez et al., GCN 43980; de Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Malesani et al., GCN 43990; Becerra et al., GCN 43991, Li et al., GCN 43993; Stein et al., GCN 43996; discovered by GOTO; O'Neill et al. 2026, TNS Discovery Report 294132) using the CAHA 1.23m telescope equipped with the DLR-MkIII CCD camera. A series of 3 x 150s exposures were taken in the BVRI bands starting at 2026-03-13T23:59:00 (~3.793 days after the Fermi trigger). The candidate is still well detected in the individual images with a preliminary AB magnitude of R = 18.3 +/- 0.1. Our photometry was calibrated using nearby stars from the Pan-STARRS catalogue and is neither corrected for Galactic extinction nor the host galaxy contribution. Comparing this new epoch with our previously reported R-band magnitude (Martin-Carrillo et al., GCN 43979) we infer a shallow decay with a power-law index of ~0.3, significantly shallower than the decay observed (~0.7) since the initial report by Konno et al., GCN 43974. These observations were made during the UCD Academy observing run at Calar Alto Observatory (Almeria, Spain) as part of the final year undergraduate projects of the University College Dublin BSc (Hons) in Physics with Astronomy and Space Science. View this GCN Circular online at https://gcn.nasa.gov/circulars/44000. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42120] Fermi GRB 260314A: Global MASTER-Net observations report
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43999 SUBJECT: Fermi GRB 260314A: Global MASTER-Net observations report DATE: 26/03/14 01:18:37 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260314A ( Fermi GBM team, GCN 43997) errorbox 83 sec after trigger time at 2026-03-14 01:00:13 UT, with upper limit up to 18.8 mag. The observations began at zenith distance = 28 deg. The sun altitude is -26.8 deg. The galactic latitude b = 34 deg., longitude l = 92 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3185241 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 93 | 2026-03-14 01:00:13 | MASTER-Kislovodsk | (17h 29m 20.27s , +62d 52m 60.0s) | C | 20 | 17.8 | 134 | 2026-03-14 01:00:54 | MASTER-Kislovodsk | (17h 29m 20.09s , +62d 53m 03.0s) | C | 20 | 17.8 | 179 | 2026-03-14 01:01:34 | MASTER-Kislovodsk | (17h 29m 19.85s , +62d 53m 05.9s) | C | 30 | 18.1 | 234 | 2026-03-14 01:02:24 | MASTER-Kislovodsk | (17h 29m 19.53s , +62d 53m 09.3s) | C | 40 | 18.4 | 300 | 2026-03-14 01:03:25 | MASTER-Kislovodsk | (17h 29m 19.14s , +62d 53m 12.2s) | C | 50 | 18.5 | 380 | 2026-03-14 01:04:35 | MASTER-Kislovodsk | (17h 29m 18.64s , +62d 53m 15.1s) | C | 70 | 18.8 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43999. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42119] Fermi GRB 260313A: Global MASTER-Net observations report
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43998 SUBJECT: Fermi GRB 260313A: Global MASTER-Net observations report DATE: 26/03/14 01:16:55 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260313A ( Fermi GBM team, GCN 43987) errorbox 31381 sec after notice time and 31405 sec after trigger time at 2026-03-13 20:43:54 UT, with upper limit up to 18.7 mag. The observations began at zenith distance = 76 deg. The sun altitude is -49.0 deg. The galactic latitude b = 39 deg., longitude l = 17 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3184597 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 91 | 2026-03-13 12:01:49 | MASTER- | (16h 26m 25.94s , +10d 37m 52.9s) | C | 20 | 19.1 | 91 | 2026-03-13 12:01:49 | MASTER- | (16h 27m 45.04s , +10d 04m 45.6s) | C | 20 | 19.3 | 121 | 2026-03-13 12:02:19 | MASTER- | (16h 26m 25.91s , +10d 36m 25.9s) | C | 20 | 19.0 | 121 | 2026-03-13 12:02:19 | MASTER- | (16h 27m 45.05s , +10d 03m 19.4s) | C | 20 | 19.2 | 156 | 2026-03-13 12:02:49 | MASTER- | (16h 26m 28.86s , +10d 38m 02.1s) | C | 30 | 19.3 | 156 | 2026-03-13 12:02:49 | MASTER- | (16h 27m 48.04s , +10d 04m 55.7s) | C | 30 | 19.6 | 201 | 2026-03-13 12:03:29 | MASTER- | (16h 26m 23.44s , +10d 37m 13.5s) | C | 40 | 19.6 | 201 | 2026-03-13 12:03:29 | MASTER- | (16h 27m 42.65s , +10d 04m 07.8s) | C | 40 | 19.7 | 256 | 2026-03-13 12:04:19 | MASTER- | (16h 26m 22.44s , +10d 38m 13.7s) | C | 50 | 19.7 | 256 | 2026-03-13 12:04:19 | MASTER- | (16h 27m 41.66s , +10d 05m 08.4s) | C | 50 | 19.8 | 321 | 2026-03-13 12:05:19 | MASTER- | (16h 26m 30.02s , +10d 37m 13.3s) | C | 60 | 19.8 | 321 | 2026-03-13 12:05:19 | MASTER- | (16h 27m 49.26s , +10d 04m 08.7s) | C | 60 | 19.9 | 397 | 2026-03-13 12:06:30 | MASTER- | (16h 26m 22.89s , +10d 36m 13.8s) | C | 70 | 19.9 | 397 | 2026-03-13 12:06:30 | MASTER- | (16h 27m 42.12s , +10d 03m 09.8s) | C | 70 | 19.9 | 914 | 2026-03-13 12:15:13 | MASTER- | (16h 27m 20.26s , +10d 02m 33.4s) | C | 60 | 19.9 | 914 | 2026-03-13 12:15:13 | MASTER- | (16h 26m 01.06s , +10d 35m 40.9s) | C | 60 | 19.7 | 1058 | 2026-03-13 12:17:36 | MASTER- | (16h 21m 46.15s , +08d 09m 04.5s) | C | 60 | 19.8 | 1058 | 2026-03-13 12:17:36 | MASTER- | (16h 20m 27.41s , +08d 42m 10.1s) | C | 60 | 19.7 | 1131 | 2026-03-13 12:18:49 | MASTER- | (16h 29m 54.57s , +08d 10m 15.0s) | C | 60 | 19.9 | 1131 | 2026-03-13 12:18:49 | MASTER- | (16h 28m 35.81s , +08d 43m 20.6s) | C | 60 | 19.7 | 1644 | 2026-03-13 12:27:23 | MASTER- | (16h 27m 24.44s , +10d 02m 47.0s) | C | 60 | 19.9 | 1644 | 2026-03-13 12:27:23 | MASTER- | (16h 26m 05.20s , +10d 35m 52.9s) | C | 60 | 19.7 | 1787 | 2026-03-13 12:29:45 | MASTER- | (16h 21m 44.33s , +08d 09m 55.3s) | C | 60 | 19.8 | 1787 | 2026-03-13 12:29:45 | MASTER- | (16h 20m 25.58s , +08d 42m 59.8s) | C | 60 | 19.7 | 1859 | 2026-03-13 12:30:57 | MASTER- | (16h 29m 49.96s , +08d 10m 36.5s) | C | 60 | 19.8 | 1859 | 2026-03-13 12:30:57 | MASTER- | (16h 28m 31.19s , +08d 43m 41.1s) | C | 60 | 19.7 | 2387 | 2026-03-13 12:39:45 | MASTER- | (16h 26m 07.46s , +10d 36m 46.3s) | C | 60 | 19.4 | 2387 | 2026-03-13 12:39:45 | MASTER- | (16h 24m 53.49s , +11d 09m 55.3s) | C | 60 | 19.5 | 2530 | 2026-03-13 12:42:08 | MASTER- | (16h 19m 23.33s , +09d 16m 12.3s) | C | 60 | 19.2 | 2530 | 2026-03-13 12:42:08 | MASTER- | (16h 20m 36.37s , +08d 43m 04.5s) | C | 60 | 19.1 | 2601 | 2026-03-13 12:43:19 | MASTER- | (16h 27m 22.55s , +09d 14m 45.8s) | C | 60 | 19.3 | 2601 | 2026-03-13 12:43:19 | MASTER- | (16h 28m 35.59s , +08d 41m 38.2s) | C | 60 | 19.0 | 3152 | 2026-03-13 12:52:30 | MASTER- | (16h 26m 13.15s , +10d 36m 57.7s) | C | 60 | 18.0 | 3152 | 2026-03-13 12:52:30 | MASTER- | (16h 24m 59.66s , +11d 10m 07.2s) | C | 60 | 18.2 | 3298 | 2026-03-13 12:54:56 | MASTER- | (16h 20m 35.88s , +08d 42m 46.2s) | C | 60 | 17.7 | 3298 | 2026-03-13 12:54:56 | MASTER- | (16h 19m 23.36s , +09d 15m 54.5s) | C | 60 | 17.8 | 3370 | 2026-03-13 12:56:08 | MASTER- | (16h 27m 25.46s , +09d 16m 34.4s) | C | 60 | 17.7 | 3370 | 2026-03-13 12:56:08 | MASTER- | (16h 28m 38.01s , +08d 43m 26.8s) | C | 60 | 17.4 | 31435 | 2026-03-13 20:43:54 | MASTER-Kislovodsk | (15h 57m 41.97s , +04d 46m 40.9s) | C | 60 | 18.1 | 31540 | 2026-03-13 20:45:38 | MASTER-Kislovodsk | (16h 01m 07.45s , +06d 40m 48.5s) | C | 60 | 18.1 | 31645 | 2026-03-13 20:47:24 | MASTER-Kislovodsk | (15h 48m 59.18s , +06d 43m 14.5s) | C | 60 | 18.1 | 31753 | 2026-03-13 20:49:11 | MASTER-Kislovodsk | (15h 55m 31.20s , +02d 53m 04.3s) | C | 60 | 18.2 | 31853 | 2026-03-13 20:50:52 | MASTER-Kislovodsk | (15h 53m 31.18s , +08d 36m 59.4s) | C | 60 | 18.3 | 31960 | 2026-03-13 20:52:39 | MASTER-Kislovodsk | (15h 54m 36.75s , +08d 36m 58.4s) | C | 60 | 12.5 | 41297 | 2026-03-13 23:28:15 | MASTER-Kislovodsk | (16h 09m 55.10s , +04d 56m 04.0s) | C | 60 | 17.9 | 41401 | 2026-03-13 23:29:59 | MASTER-Kislovodsk | (16h 05m 46.45s , +08d 42m 26.9s) | C | 60 | 18.5 | 41506 | 2026-03-13 23:31:44 | MASTER-Kislovodsk | (16h 07m 41.96s , +03d 01m 52.5s) | C | 60 | 18.3 | 41604 | 2026-03-13 23:33:22 | MASTER-Kislovodsk | (16h 13m 25.35s , +06d 48m 48.5s) | C | 60 | 18.4 | 41707 | 2026-03-13 23:35:05 | MASTER-Kislovodsk | (15h 59m 05.81s , +10d 38m 10.3s) | C | 60 | 18.7 | 41820 | 2026-03-13 23:36:58 | MASTER-Kislovodsk | (15h 43m 40.10s , +03d 02m 39.4s) | C | 60 | 18.1 | 42252 | 2026-03-13 23:44:10 | MASTER-Kislovodsk | (15h 54m 29.49s , +01d 08m 26.1s) | C | 60 | 18.5 | 42360 | 2026-03-13 23:45:58 | MASTER-Kislovodsk | (15h 41m 30.91s , +08d 43m 08.7s) | C | 60 | 18.6 | 42478 | 2026-03-13 23:47:56 | MASTER-Kislovodsk | (15h 37m 05.30s , +06d 50m 16.8s) | C | 60 | 18.6 | 42581 | 2026-03-13 23:49:39 | MASTER-Kislovodsk | (15h 46m 50.58s , +10d 36m 59.0s) | C | 60 | 18.6 | 42681 | 2026-03-13 23:51:19 | MASTER-Kislovodsk | (16h 06m 25.20s , +01d 06m 49.4s) | C | 60 | 18.4 | 42802 | 2026-03-13 23:53:20 | MASTER-Kislovodsk | (16h 11m 16.05s , +10d 36m 20.0s) | C | 60 | 18.4 | 42914 | 2026-03-13 23:55:12 | MASTER-Kislovodsk | (16h 12m 12.42s , +10d 36m 20.3s) | C | 60 | 13.0 | 43021 | 2026-03-13 23:56:59 | MASTER-Kislovodsk | (16h 13m 46.32s , +10d 36m 17.0s) | C | 60 | 12.9 | 43195 | 2026-03-13 23:59:53 | MASTER-Kislovodsk | (16h 19m 39.08s , +03d 02m 31.4s) | C | 60 | 18.3 | 43305 | 2026-03-14 00:01:43 | MASTER-Kislovodsk | (15h 33m 51.88s , +04d 55m 55.3s) | C | 60 | 18.1 | 43425 | 2026-03-14 00:03:43 | MASTER-Kislovodsk | (15h 42m 27.14s , +01d 09m 22.2s) | C | 60 | 18.2 | 43540 | 2026-03-14 00:05:39 | MASTER-Kislovodsk | (15h 53m 26.55s , +12d 31m 34.8s) | C | 60 | 18.3 | 43643 | 2026-03-14 00:07:21 | MASTER-Kislovodsk | (16h 25m 31.18s , +06d 50m 11.1s) | C | 60 | 17.6 | 43748 | 2026-03-14 00:09:06 | MASTER-Kislovodsk | (16h 05m 42.64s , +12d 31m 14.8s) | C | 60 | 18.1 | 43962 | 2026-03-14 00:12:40 | MASTER-Kislovodsk | (15h 54m 17.96s , -00d 44m 27.8s) | C | 60 | 12.1 | 46601 | 2026-03-14 00:56:39 | MASTER-Kislovodsk | (16h 06m 19.90s , -00d 45m 06.5s) | C | 60 | 17.9 | 46699 | 2026-03-14 00:58:17 | MASTER-Kislovodsk | (16h 18m 28.04s , +01d 10m 17.3s) | C | 60 | 18.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43998. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42118] GRB 260314A: Fermi GBM Final Real-time Localization
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43997 SUBJECT: GRB 260314A: Fermi GBM Final Real-time Localization DATE: 26/03/14 01:09:31 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 00:58:50 UT on 14 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260314A (trigger 795142735.353478 / 260314041). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 260.2, Dec = 62.9 (J2000 degrees, equivalent to J2000 17h 20m, 62d 53'), with a statistical uncertainty of 8.2 degrees. The angle from the Fermi LAT boresight is 59.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260314041/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260314041/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260314041/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43997. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42117] GRB 260310A/AT 2026fgk: WINTER NIR Detections
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43996 SUBJECT: GRB 260310A/AT 2026fgk: WINTER NIR Detections DATE: 26/03/13 21:05:01 GMT FROM: Robert David Stein at JSI <rdstein(a)umd.edu> Robert Stein (UMD), Geoffrey Mo (Caltech/Carnegie), Viraj Karambelkar (Columbia), Xander J. Hall (CMU), Tomas Ahumada (NOIRLab), Danielle Frostig (CfA), Mansi Kasliwal (Caltech), Nathan Lourie (MIT), Benjamin Schneider (LAM), Robert Simcoe (MIT), and report: We observed AT 2026fgk (Konno et al., GCN 43974; Hinds et al., AstroNote 2026-65; O’Neill et al. 2026, TNS Discovery Report 294132), identified as the likely counterpart to GRB 260310A (Fermi GBM Team, GCN 43951). We used the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations began at 2026-03-12T09:57:09.115 UTC (~53 hours after the GRB trigger), and continued over several expochs in both J-band and Hs-band. 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) We clearly detect a source in all of our stacked images, with times given relative to burst time (2026-03-10T04:57:11): | t - t0 (hr) | filter | mag(AB) | magerr | limiting mag | |-------------|--------|---------|--------|--------------| | 53.00 | J | 17.16 | 0.09 | 19.28 | | 53.58 | J | 17.28 | 0.09 | 19.18 | | 54.13 | Hs | 17.10 | 0.21 | 17.91 | | 71.87 | J | 17.34 | 0.12 | 19.03 | | 72.17 | Hs | 16.97 | 0.20 | 17.77 | We do not perform image subtraction due to a lack of suitable reference images, so there might be some contamination from the host galaxy. However, given the large offset and relatively faint host, we do not expect this to substantially alter our measurements. We do not measure significant evolution over our ~20 hour baseline, after accounting for the uncertainty in each measurement. A slow fading would be consistent with these observations, and with expectations for a power-law decay of an afterglow at this relatively late (>2 days) phase. Our observations are consistent with values reported by Li et al (GCN 43993), who quote a value of J=16.7 +/- 0.1 mag in the Vega system (~17.6 mag AB) at a later phase of +81 hours. Further observations of this transient are planned. 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/43996. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42116] GRB 260313A: A Correction to the Fermi GBM Final Localization
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43995 SUBJECT: GRB 260313A: A Correction to the Fermi GBM Final Localization DATE: 26/03/13 18:31:37 GMT FROM: oliver.roberts(a)universityofgalway.ie O.J. Roberts (Uni. of Galway, Ireland) reports on behalf of the Fermi Gamma-ray Burst Monitor Team. "At 12:00:28.58 UT on 13 March 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260313A (trigger 795096033/260312500). An on-ground calculated location, using the Fermi GBM trigger data, was initially reported in GCN 43987 by the GBM Team. Further analysis found the location of the short GRB to be inaccurate. We report the updated/refined location to be RA = 241.16, Dec = 5.80 (J2000 degrees, equivalent to J2000 16h 05m, 05d 48'), with a statistical uncertainty of 5.8 degrees. The angle from the Fermi LAT boresight with this new position is 15 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260312500/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260312500/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260312500q…" View this GCN Circular online at https://gcn.nasa.gov/circulars/43995. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42115] GRB 260310A: Einstein Probe Follow-up X-ray Telescope (FXT) Detection
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43994 SUBJECT: GRB 260310A: Einstein Probe Follow-up X-ray Telescope (FXT) Detection DATE: 26/03/13 17:39:34 GMT FROM: Rahul Jayaraman at Cornell University <rj438(a)cornell.edu> Rahul Jayaraman (Cornell), Anna Y. Q. Ho (Cornell), K-Ryan Hinds (Caltech), S. Y. Fu (HUST), R. D. Liang, M. J. Liu, Z. X. Ling, Hui Sun, Weimin Yuan (NAO, CAS), Genevieve Schroeder (Cornell), Xander J. Hall (CMU), Michael Coughlin (UMN) report: The Follow-up X-ray Telescope on board the Einstein Probe observed the position of AT2026fgk, the likely counterpart to GRB 260310A (Fermi GBM team, GCN 43951; Arya et al., GCN 43958; Konno et al., GCN 43974; Martin-Carrillo et al., GCN 43979; Méndez et al., GCN 43980; Becerra et al., GCN 43991), beginning at 2026-03-12T17:22:58 UTC. The exposure time of this observation was 1498 s. An uncatalogued X-ray source was detected at RA = 219.3158, DEC = 71.8417, with an uncertainty of 10 arcsec (radius, 90% CL statistical and systematic); this X-ray source is consistent with the optical position initially reported by Hinds et al., AstroNote 2026-65. We performed a preliminary analysis of the FXT spectrum in the 0.5-10 keV energy range from both the A and B modules. We fit an absorbed power-law with a line-of-sight hydrogen column density of 2.65 x 10^20 cm^-2. We find a photon index of 1.55 ± 0.09, with an unabsorbed flux of (5.51 ± 0.22) x 10^-12 erg/s/cm^2. At the redshift of z = 0.153 from Ugarte Postigo et al. (GCN 43984), this would correspond to an X-ray luminosity of (3.74 ± 0.15) x 10^44 erg/s. Parameter uncertainties are reported at the 90% C.L. We consider this source the likely X-ray afterglow to GRB 260310A, and encourage further follow-up. The Einstein Probe is a space mission supported by the Strategic Priority Program on Space Sciénce of the Chinese Academy of Sciences, in collaboration with the European Space Agency, the Max-Planck-Institute for Extraterrestrial Physics (Germany), and the Centre National d'études Spatiales (France). View this GCN Circular online at https://gcn.nasa.gov/circulars/43994. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42114] GRB 260310A/AT 2026fgk: J-band observations by the SYSU 80 cm infrared telescope
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43993 SUBJECT: GRB 260310A/AT 2026fgk: J-band observations by the SYSU 80 cm infrared telescope DATE: 26/03/13 17:35:21 GMT FROM: lijj328(a)mail2.sysu.edu.cn Jin-Ji Li, Chun Chen, Duo-Le Cao, Zhong-Nan Dong, Wei-Sen Huang, Jia-Qi Lin, Pu Lin, Yun Shi, Hao-Nan Yang, Yan Yu, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm infrared telescope team: We observed the field of GRB 260310A (Fermi GBM Team, GCN 43951; Salunke et al., GCN 43958), using the Sun Yat-sen University (SYSU) 80 cm infrared telescope. Our observations were carried out on 2026 Mar 13, 13:58 UT, 81.0 hours after the GRB trigger, using stacked images in the J band. We clearly detect an infrared counterpart at the position of the optical afterglow candidate AT 2026fgk (Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979; Moreno Méndez et al., GCN 43980; Atteia et al., GCN 43981; de Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Malesani et al., GCN 43990; Becerra et al., GCN 43991; discovered by GOTO; O'Neill et al. 2026, TNS Discovery Report 294132), and we measure J = 16.7±0.1 Vega mag. The photometry was calibrated against nearby stars from the 2MASS catalog and is reported in the Vega system, without correction for Galactic extinction. The SYSU 80 cm infrared telescope is operated and managed by the Department of Astronomy, Sun Yat-sen University. View this GCN Circular online at https://gcn.nasa.gov/circulars/43993. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42113] GRB 260310B: Insight-HXMT/HE detection
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43992 SUBJECT: GRB 260310B: Insight-HXMT/HE detection DATE: 26/03/13 15:05:40 GMT FROM: renyz16607(a)163.com Yang-Zhao Ren, Chen-Wei Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng (IHEP) report on behalf of the Insight-HXMT team: At 2026-03-10T21:41:23.850 (T0), Insight-HXMT/HE detected a long burst, GRB 260310B, which is also detected by Fermi/GBM (Fermi GBM team, GCN #43955), and GECAM-B (Ren et al., GCN #43967). The Insight-HXMT/HE light curve mainly consists of multi-pulses with T90 of 43.5 +5.5/-7.5 s. The 1s peak rate, measured from T0+0.25 s, is 1147 cnts/sec. Insight-HXMT/HE detected a total of 11204 counts from this burst. The Insight-HXMT /HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb260310B.png All measurements above are made with the CsI detectors of Insight-HXMT/HE operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://hxmten.ihep.ac.cn/ View this GCN Circular online at https://gcn.nasa.gov/circulars/43992. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42112] GRB 260310A/AT 2026fgk: DDOTI Optical Detection
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43991 SUBJECT: GRB 260310A/AT 2026fgk: DDOTI Optical Detection DATE: 26/03/13 14:38:23 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), 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), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report: We observe the field of the Fermi/GBM GRB 260310A (Fermi GBM Team, GCN 43951) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the nights of 2026-03-10 and 2026-03-11 UTC. DDOTI observed from 05:11 UTC to 9:34 on 2026-03-10 (from T+0.2 hours to T+4.6 hours after the trigger) with a total exposure time of 2.1 hours and from 03:32 UTC to 12:20 on 2026-03-11 (from T+22.6 hours to T+31.4 hours after the trigger), with a total exposure time of 3.1 hours. On both nights we detect the source AT2026fgk (discovered by GOTO; O’Neill et al. 2026, TNS Discovery Report 294132), proposed as the optical counterpart (Konno et al.; GCN Circ. 43974), with preliminary AB magnitudes of: w ≈ 16.6 (in our first epoch); w = 17.52 +/- 0.01 (in our second epoch). The photometry of the second night is consistent with a temporal decay of alpha≈-0.6 between the magnitudes reported by the LAST collaboration (Konno et al.; GCN Circ. 43974) and COLIBRÍ (Moreno Méndez et al.; GCN Circ. 43980). Due to technical problems during the first night, the photometry from that epoch should be considered tentative. These values are 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/43991. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42111] GRB 260310A: NOT optical polarimetry
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43990 SUBJECT: GRB 260310A: NOT optical polarimetry DATE: 26/03/13 14:33:29 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> M. Pursiainen (Warwick), D. B. Malesani (DAWN/NBI and Radboud), G. Leloudas (DTU Space), Dimple (Birmingham), A. Martin-Carrillo (UCD), B. P. Gompertz (Birmingham), D. A. Perley (LJMU), N. Pyykkinen (NOT and UTU), report on behalf of a larger collaboration: We observed the likely optical counterpart AT 2026fgk (Konno et al., GCN 43974; Hinds et al., AstroNote 2026-65; O’Neill et al. 2026, TNS Discovery Report 294132) of GRB 260310A (Hamburg & Meegan, GCN 43975; Salunke et al., GCN 43958), using the Nordic Optical Telescope (NOT) equipped with ALFOSC, carrying out imaging polarimetry. In an image taken on 2026 Mar 13.09 UT (2.89 days after trigger), the transient had an AB magnitude of r = 18.12 +- 0.02 (calibrated against Pan-STARRS sources, not corrected for Galactic extinction). Unfortunately the seeing conditions were poor (~2.8" FWHM). A sequence of 4x900 s exposures was secured in linear imaging polarimetry (mean epoch Mar 13.09 UT), employing four different retarder plate angles and an SDSS r filter. The data were reduced with a custom-built reduction pipeline (Pursiainen et al. 2025, doi:10.1093/mnras/staf232) based on the photutils python library (Bradley et al. 2024, doi:10.5281/zenodo.13989456), with reduction steps detailed in Pursiainen et al. (2023, doi:10.1051/0004-6361/202345945). No significant polarization is found for the transient, down to a 3-sigma upper limit of P < 1.5%. No correction for Galactic interstellar polarization has been applied, though we note that the line of sight to GRB 260310A only suffers from very modest extinction (A_V = 0.05 mag). View this GCN Circular online at https://gcn.nasa.gov/circulars/43990. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42110] GRB 260312B: AstroSat CZTI detection
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43989 SUBJECT: GRB 260312B: AstroSat CZTI detection DATE: 26/03/13 13:07:30 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Goyal (IITB), A. Arya (IITB), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (IUCAA), G. Waratkar (Caltech/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 GRB 260312B which was also detected by Fermi GBM (Fermi GBM Team , GCN Circ. 43969), and Glowbug (Cheung et. al., GCN Circ. 43976). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-03-12 09:46:53.50 UTC. The measured peak count rate associated with the burst is 131 (+29, -30) counts/s above the background in the combined data of three quadrants (out of four), with a total of 605 (+164, -182) counts. The local mean background count rate was 186 (+3, -4) counts/s. Using cumulative rates, we measure a T90 of 14 (+1, -6) s. The source was also faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. 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/43989. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42109] Swift BAT trigger 1500295: A solar flare
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43988 SUBJECT: Swift BAT trigger 1500295: A solar flare DATE: 26/03/13 12:49:55 GMT FROM: Amy <yarleen(a)gmail.com> C. Gronwall (PSU), R. Gupta (NASA GSFC) and A. Y. Lien (U Tampa) report on behalf of the Neil Gehrels Swift Observatory Team: BAT trigger 1500295 is not a GRB, but was caused by a solar flare. Swift's automatic slews are currently disabled, so there will be no XRT or UVOT data for this trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/43988. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42108] GRB 260313A: Fermi GBM Final Real-time Localization
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43987 SUBJECT: GRB 260313A: Fermi GBM Final Real-time Localization DATE: 26/03/13 12:11:03 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 12:00:28 UT on 13 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260313A (trigger 795096033.584074 / 260313500). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 53.4, Dec = 33.3 (J2000 degrees, equivalent to J2000 03h 33m, 33d 17'), with a statistical uncertainty of 14.1 degrees. The angle from the Fermi LAT boresight is 152.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260313500/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260313500/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260313500/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43987. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42107] GRB 260310A/AT 2026fgk: Bok spectroscopic observation
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43986 SUBJECT: GRB 260310A/AT 2026fgk: Bok spectroscopic observation DATE: 26/03/13 11:30:56 GMT FROM: Brian Hsu at University of Arizona <bhsu(a)arizona.edu> B. Hsu (U of Arizona), M. Shrestha (Monash U), Jennifer Andrews (Gemini-N/NOIRLab), D. J. Sand (U of Arizona), N. Franz (U of Arizona), J. Pearson (U of Arizona), C. Christy (U of Arizona), C. L. Ransome (U of Arizona), Bhagya Subrayan (U of Arizona), K. Bostroem (U of Arizona), G. Hosseinzadeh (UCSD), N. Smith (U of Arizona) We observed the possible optical counterpart to GRB 20260310A/AT2026fgk (Konno et al., GCN 43974; Lipunov et al., GCN 43978, discovered by GOTO; O'Neill et al. 2026, TNS Discovery Report 294132) on UT 2025-03-13T06:02:23.850 using the B&C spectrograph on the 90-inch Bok telescope. The optical counterpart is clearly visible. The optical spectrum shows a featureless red continuum, although there is a strong, narrow emission line at 5571 Angstroms that we attribute to H-beta from the candidate host galaxy at z = 0.146, which is in agreement with the redshift obtained by Hinds et al., GCN 43977. Additional follow-up observations are encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/43986. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42106] Swift BAT trigger 1500287: A solar flare
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43985 SUBJECT: Swift BAT trigger 1500287: A solar flare DATE: 26/03/13 11:28:17 GMT FROM: Amy <yarleen(a)gmail.com> P. A. Evans (U Leicester), C. Gronwall (PSU), R. Gupta (NASA GSFC) and A. Y. Lien (U Tampa) report on behalf of the Neil Gehrels Swift Observatory Team: BAT trigger 1500287 is not a GRB, but was caused by a solar flare. Swift's automatic slews are currently disabled, so there will be no XRT or UVOT data for this trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/43985. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42105] GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43984 SUBJECT: GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153 DATE: 26/03/13 11:16:28 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> A. de Ugarte Postigo (LAM), L. Izzo (INAF/OACN and DARK/NBI), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), S. Geier (GTC), C. C. Thoene (AbAO), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), G. Lombardi (GTC), N. A. Rakotondrainibe (LAM), B. Schneider (LAM), N. R. Tanvir (Univ. Leicester), D. A. Perley (LJMU), F. M. Pérez Toledo (GTC), D. Pérez Valladares (GTC) report: We observed AT2026fgk (a.k.a. GOTO26buh, O’Neill et al. 2026, TNS Discovery Report 294132; Hinds et al., AstroNote 2026-65), proposed as the optical counterpart (Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979; Moreno Méndez et al., GCN 43979) of GRB 260310A (Hamburg & Meegan, GCN 43975; Salunke et al., GCN 43958) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ instrument. The seeing conditions were very poor (3.5" measured in the acquisition image). In the 30-s acquisition image (beginning on 2026-03-13 at 04:23:43 UT, that is 2.98 days after trigger), the optical afterglow is well detected with a magnitude r = 18.05 + 0.05 (AB), calibrated against nearby Pan-STARRS objects, and not corrected for Galactic extinction. We warn that, given the poor seeing, some contamination from the nearby galaxy cannot be excluded. A total of 3x600 s spectra were secured in each of grism R1000B (3600-7800 AA) and R1000R (5100-10000 AA), with mean epoch 2026-03-13 at 04:58:13 UT (3.00 days after trigger). The slit covers both the optical transient and the core of the nearby galaxy. Continuum is visible over the entire range 3600-10000 AA. We detect a number of emission features that extend from the galaxy core to the location of the transient, with a typical drift due to galaxy rotation. These features include [O II], [O III], H-beta, H-alpha, [N II] and [SII] at a redshift of z = 0.153, confirming, and consolidating, the measurement by Hinds et al. (GCN 43977). No absorption features are detected either at the emission redshift (no Ca II, Ca I or Na I) nor in any other part of the spectrum. The lack of Mg II detection (typically the strongest feature in GRB afterglow spectra) in our spectral range would discard a redshift larger than 0.3 for a long GRB sight line with typical line strengths (using as reference the sample of de Ugarte Postigo et al. 2012, doi:10.1051/0004-6361/201219894). In particular at a redshift of 0.3, where the SNR would be worse, Mg II would have to be fainter than 95% of the GRB sight lines. At z = 0.7, this line of sight would need to be weaker than any in the sample. Furthermore, the chance probability of a transient appearing within 5" from the galaxy without being related is just ~1% (Moreno Méndez et al., GCN 43979). All of this indicates that the transient is indeed at the redshift of z = 0.153. The GRB afterglow is located in the outskirts of a galaxy, at a projected distance of ~13.5 kpc from the galaxy core. This offset is very large for a GRB from a collapsar origin and more in line with the expectations for mergers (e.g. Fong et al. 2022, doi: 10.3847/1538-4357/ac91d0), although not unprecedented even for collapsars (see e.g. Thoene et al. 2024, doi:10.1051/0004-6361/202348141). Together with the location in the merger region of the Epeak - Eiso diagram (Atteia et al., GCN 43981), this opens the possibility that GRB 260310A had a merger progenitor. Further monitoring to constrain the emergence of an associated SN will clarify the nature of the source and is strongly encouraged. This work has used the GRBspec database at http://grbspec.eu (de Ugarte Postigo et al. 2014, doi:10.1117/12.2055774). View this GCN Circular online at https://gcn.nasa.gov/circulars/43984. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42104] GRB 260308A: Insight-HXMT/HE detection
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43983 SUBJECT: GRB 260308A: Insight-HXMT/HE detection DATE: 26/03/13 11:02:02 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> Xing-Hao Luo, Chen-Wei Wang, Chao Zheng, Hao-Xuan Guo, Xiao-Bo Li and Shao-Lin Xiong (IHEP) report on behalf of the Insight-HXMT team: At 2026-03-08T20:05:53.000 (T0), Insight-HXMT/HE detected the burst GRB 260308A, which is also detected by Fermi/GBM (Fermi GBM Team, GCN #43949) and SVOM/GRM (Xing-Hao Luo et.al., GCN#43960). The Insight-HXMT/HE light curve mainly consists of a single pulse with a T90 of 0.3 +0.2/-0.1 s. The 1s peak rate, measured from T0-0.65 s, is 625 cnts/sec. Insight-HXMT/HE detected a total of 512 counts form this burst. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb260308A.png All measurements above are made with the CsI detectors of Insight-HXMT/HE operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://hxmten.ihep.ac.cn/ View this GCN Circular online at https://gcn.nasa.gov/circulars/43983. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42103] GRB 260307A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43982 SUBJECT: GRB 260307A: CALET Gamma-Ray Burst Monitor detection DATE: 26/03/13 10:45:12 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> Y. Shimizu (Kanagawa U), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), 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 260307A (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN Circ. 43939; Glowbug gamma-ray detection: Cheung et al., GCN Circ. 43950; GECAM-B observation: Zao et al., GCN Circ. 43961) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 11:27:56.49 UTC on 7 March 2026 (https://cgbm.calet.jp/cgbm_trigger/flight/1456918069/index.html) The burst signal was seen by all CGBM detectors. The burst light curve shows a multi-peaked structure that starts at T+2.8 sec, peaks at T+5.2 sec, and ends at T+8.0 sec. The T90 and T50 durations measured by the SGM data are 4.6 +/- 0.5 sec and 2.0 +/- 0.2 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1456918069/ 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/43982. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42102] GRB 260310A / AT 2026fgk: Location in the Epeak - Eiso diagram
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43981 SUBJECT: GRB 260310A / AT 2026fgk: Location in the Epeak - Eiso diagram DATE: 26/03/13 08:04:42 GMT FROM: Jean-Luc Atteia at IRAP <jean-luc.atteia(a)irap.omp.eu> Jean-Luc Atteia (IRAP), Enrique Moreno Méndez (UNAM), Massimiliano Lincetto (CPPM), Damien Dornic (CPPM), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Camila Angulo (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report: we computed the isotropic equivalent energy of GRB 260310A (Fermi GBM Team, GCN Circ. 43951) , using the spectral information on the prompt emission measured by Fermi GBM (Hamburg & Meegan, GCN Circ. 43975), in order to locate the GRB in the Amati diagram. At z = 0.153 (Hinds et al. GCN 43977), Ep,i = 198 keV, Eiso = 3.5e50 erg and GRB 260310A clearly lies in the Type I (mergers) region of the Amati plot, which is unusual for a long GRB. In order to locate GRB 260310A in the Type II (collapsars) region of the Amati plot, it has to be at z ≥ 0.7, and not associated with the bright galaxy noticed by the LAST team (Konno et al., GCN Circ. 43974). View this GCN Circular online at https://gcn.nasa.gov/circulars/43981. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42101] GRB 260310A / AT 2026fgk: COLIBRÍ optical observations
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43980 SUBJECT: GRB 260310A / AT 2026fgk: COLIBRÍ optical observations DATE: 26/03/13 04:01:22 GMT FROM: enriquemm(a)astro.unam.mx Enrique Moreno Méndez (UNAM), Massimiliano Lincetto (CPPM), Damien Dornic (CPPM), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Camila Angulo (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM),, and Antonio de Ugarte Postigo (LAM) report: We imaged the field of AT 2026fgk (Lipunov et al., GCN Circ. 43954; Konno et al., GCN Circ. 43975; Hinds et al., GCN Circ. 43977; Lipunov et al., GCN Circ. 43978, Martin-Carrillo et al., GCN Circ. 43079), a possible counterpart of the Fermi GBM GRB 260310A (Fermi GBM Team, GCN Circ. 43951; Humburg & Meegan, GCN Circ. 43975) and also detected by AstroSat CZTI (Salunke et al., GCN Circ. 43958), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-13 02:37 to 03:06 UTC (from 69.67 to 70.15 hours after the GRB trigger) and obtained 8, 8, 8, 8, and 16 minutes, respectively, of exposure in the g, r, i, z, and y filters. The data were reduced, coadded, calibrated, and analysed with the ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked images, we detect AT 2026fgk with preliminary PSF magnitudes of: g = 18.53 +/- 0.01 r = 18.15 +/- 0.01 i = 17.95 +/- 0.01 z = 17.74 +/- 0.01 y = 17.63 +/- 0.02 Our photometry is consistent with the reported by Martin-Carrillo (GCN Circ. 43979) and with the colours expected for a low-redshift GRB, supporting its association with GRB 260310A (Fermi GBM Team, GCN Circ. 43951). As was firstly noticed by the LAST team (Konno et al.; GCN Circ. 43974), this source is projected separation of 11.3 kpc from the center of a nearby galaxy with photo-z ≈ 0.11 (Legacy Survey DR10, Dey et al. 2019) and likely spectroscopic redshift z = 0.153 (Hinds et al., GCN Circ. 43977). This source has a probability of chance alignment with the nearby galaxy of <1%, strongly suggesting an association. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/43980. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42100] GRB 260310A / AT2026fgk: CAHA 1.23m telescope optical observations
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43979 SUBJECT: GRB 260310A / AT2026fgk: CAHA 1.23m telescope optical observations DATE: 26/03/13 02:28:03 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> A. Martin-Carrillo, J. Roca Garcia-Valino, E. Aasen, L. Brown, D. Colfer, M. Collins, J. Costello, C. Harris, R. Odunuga, H. O'Leary Jeffers, C. O'Malley, J. Parimkayala, R. Roddy, D. Scott, A. Valdivia y Alvarado Carvajal (UCD), J. F. Agui Fernandez (CAHA), A. Fernandez-Martin (CAHA) report on behalf of a larger collaboration: We observed the optical counterpart candidate (Konno et al., GCN 43974; Lipunov et al. GCN 43978, discovered by GOTO; O'Neill et al. 2026, TNS Discovery Report 294132) of GRB 260310A (Fermi GBM Team, GCN 43951; Salunke et al. 2026, GCN 43958) using the CAHA 1.23m telescope equipped with the DLR-MkIII CCD camera. A series of 3 x 150s exposures were taken in the BVR bands starting at 2026-03-12T22:57:09 (~2.75 days after the Fermi trigger). The candidate is well detected in the individual images with a preliminary AB magnitude of R = 18.2 +/- 0.1. Our photometry was calibrated using nearby stars from the Pan-STARRS catalogue and is not corrected for Galactic extinction. It should be noted that it is likely that this value has some contribution from the nearby likely host galaxy. These observations were made during the UCD Academy observing run at Calar Alto Observatory (Almeria, Spain) as part of the final year undergraduate projects of the University College Dublin BSc (Hons) in Physics with Astronomy and Space Science. View this GCN Circular online at https://gcn.nasa.gov/circulars/43979. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42099] GRB 260310A / AT2026fgk : MASTER OT rebrightening during 7h observations
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43978 SUBJECT: GRB 260310A / AT2026fgk : MASTER OT rebrightening during 7h observations DATE: 26/03/13 02:18:22 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov (Lomonosov MSU), N.Budnev, O.Gress (ISU), A.Kuznetsov, I.Panchenko, P.Balanutsa, G.Antipov, E.Gorbovskoy, N.Tiurina, Ya.Kechin, V.Senik, A.Chasovnikov, M.Shilova,V.Topolev, D.Vlasenko, A.Sankovich, Yu.Tselik (Lomonosov MSU), D.Svinkin (Ioffe Institute), M.J. Segura, 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), 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, J.Tanori, L. Villalobos, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) MASTER Global Robotic Net [1-4] started Fermi GRB 260310A observations (Fermi team GCN 43951) at MASTER-Tunka robotic telescope at 2026-03-10 16:01:36 UT (Lipunov et al. GCN 43954) Optical transient AT2026fgk, discovered by GOTO at 2026-03-10 05:14:30.624 (TNSC 1001, https://www.wis-tns.org/object/2026fgk ) was detected as MASTER OT J143716.19+715031.2 at our images at 2026-03-12 13:46:11UT with m_unfiltered~18.3. This OT was observed at 400 images with rebrigtening detection to 17.2 at 2026-03-12 21:02:59 UT. Observation and reduction will continue. [1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L [2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271 [3] Lipunov et a. 2019, ARep, vol.63, 293 [4] Lipunov et al. 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics,Lomonosov MSU PRESS, 591pp. http://www.pereplet.ru/lipunov/625.html#625 View this GCN Circular online at https://gcn.nasa.gov/circulars/43978. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42098] GRB260310A / AT2026fgk: P200 Spectroscopy
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43977 SUBJECT: GRB260310A / AT2026fgk: P200 Spectroscopy DATE: 26/03/13 00:27:51 GMT FROM: khinds(a)caltech.edu K-Ryan Hinds (Caltech), Daniel A. Perley (LJMU), Anna Y. Q. Ho (Cornell), Sam Rose (Caltech), Jillian Rastinejad (UMd), Robert Stein (UMd), Geoffrey Mo (Caltech), Mansi Kasliwal (Caltech), Jesper Sollerman (OKC), Xander J. Hall (CMU), Jacob Wise (LJMU), Rahul Jayaraman (Cornell), Aleksandra Bochenek (LJMU) We previously reported the optical transient AT 2026fgk (ID 294132) as an afterglow candidate based on its fast evolution, red color, and high implied luminosity (Hinds et al., AstroNote 2026-65). Konno et al. (GCN 43974) reported additional detections of AT 2026fgk using the Large Array Survey Telescope (LAST) whilst tiling the probability region for GRB 260310A (Fermi GBM Team, GCN 43951; Salunke et al., GCN 43958), and noted the temporal and spatial coincidence that identifies AT 2026fgk as the likely optical counterpart of this GRB. We observed GRB 260310A starting at 2026-03-12 10:23:42 UTC (~2.2 d after the Fermi GBM trigger time) with the Next Generation Palomar Spectrograph (NGPS; AstroNote 2024-340) on the Palomar 5.1m Hale Telescope (P200). The optical spectrum shows a featureless red continuum, although there is a strong, narrow emission line at 7566 Angstroms that we attribute to H-alpha from the candidate host galaxy at z = 0.153. If this is the redshift of the GRB, it would be among the closest long-duration bursts to date. For GRB 260310A, using a fluence of 5.8e-6 erg/cm^2 (10-1000 keV) reported by Hamburg et al. (GCN 43795) and assuming the redshift above, we find the gamma-ray E_iso is ~3.69e50 erg, characteristic of low-luminosity long-GRBs. The peak observed optical luminosity (from ATLAS forced photometry) is M_o ~ -22.7 mag at 7.2 hours post-trigger, more luminous than the equivalent value seen in most other nearby LLGRBs. An associated supernova similar to SN 1998bw would peak at an apparent magnitude of r = 19.7 at this redshift in the absence of host extinction. Further observations are encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/43977. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42097] GRB 260312B: Glowbug gamma-ray detection
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43976 SUBJECT: GRB 260312B: Glowbug gamma-ray detection DATE: 26/03/12 23:50:31 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260312B, which was also detected by Fermi/GBM (GCN 43969, 43970). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-03-12 09:46:45.000 with a duration of 12.3 s and a total significance of about 43 sigma. The light curve comprises a faint peak at ~T0+1s and a primary peak at ~T0+7s. Note that data from ~T0+4.0s to +6.0s and ~T0+10.0s to +11.5s suffered from deadtime in various detectors. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/43976. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42096] GRB 260310A: Fermi GBM Observation
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43975 SUBJECT: GRB 260310A: Fermi GBM Observation DATE: 26/03/12 22:19:13 GMT FROM: rhamburg(a)usra.edu R. Hamburg (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 04:57:10.81 UT on 10 March 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260310A (trigger 794811435/260310206), which was also detected by AstroSat (Salunke et al. 2026, GCN 43958). This GRB has been reported to have a potential optical counterpart, AT2026fgk, which was discovered by GOTO (O'Neill et al. 2026, TNS Discovery Report 294132) and LAST (Konno et al. 2026, GCN 43974). AT2026fgk has a photometric redshift measurement of z = 0.11 (Hinds et al. 2026, AstroNote 2026-65). The angle from the Fermi LAT boresight is 124 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 60 s (50-300 keV). The time-averaged spectrum from T0-9.6 to T0+61.6 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.15 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 172 +/- 5 keV. The event fluence (10-1000 keV) in this time interval is (5.8 +/- 0.4)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+9.8 s in the 10-1000 keV band is 2.3 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/43975. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42095] GRB 260310A: potential optical counterpart
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43974 SUBJECT: GRB 260310A: potential optical counterpart DATE: 26/03/12 19:11:47 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), and S. Spitzer (WIS) report on behalf of the LAST Collaboration. We report observations of GRB 260310A, detected by Fermi/GBM (Fermi GBM Team, GCN 43951), as well as by AstroSat/CZTI (Salunke et al., GCN 43958). Observations were conducted with the Large Array Survey Telescope (LAST; Ofek et al. 2023, PASP 135, 5001; Ben-Ami et al. 2023, PASP 135, 5002). Observations of GRB 260310A were taken over several tiling epochs starting at 2026-03-10 16:37:45 UTC (T-T0 = 11.67 h), in clear band (similar to the Gaia Bp band) with 24 telescopes. Each epoch consists of 20x20s exposures per telescope. The follow-up covers an integrated localization probability of 97% as given within the HEALPix FITS file glg_healpix_all_bn260310206.fit (Fermi GBM Team, GCN 43951). Initially, we do not detect a credible counterpart within our automated pipeline due to incomplete reference coverage of the field. However, we note AT 2026fgk (discovered by GOTO; O'Neill et al. 2026, TNS Discovery Report 294132) as a potential counterpart. The transient was first detected at T-T0 = 1040 s, has an angular separation of about 7 deg from the best-fit Fermi/GBM position, and is shown to be highly variable (Hinds et al., AstroNote 2026-65). This transient is clearly detected within the LAST data and shows an initial rise and a subsequent steady decay, consistent with Hinds et al., AstroNote 2026-65. The LAST photometry is as follows | Tmid-T0 (h) | Mag (AB) | | ------------ | ------------ | | 14.05 | 17.18 +/- 0.04 | | 14.17 | 17.17 +/- 0.04 | | 14.30 | 17.09 +/- 0.04 | | 14.41 | 17.16 +/- 0.04 | | 14.54 | 17.10 +/- 0.04 | | 14.66 | 17.11 +/- 0.04 | | 17.97 | 17.23 +/- 0.04 | | 19.01 | 17.25 +/- 0.04 | | 20.05 | 17.19 +/- 0.04 | | 21.09 | 17.30 +/- 0.04 | | 22.02 | 17.32 +/- 0.04 | Furthermore, serendipitous LAST observations of the field prior to the GRB event time, up to 2026-03-10 02:51:01 UTC (T-T0 = -2.15 h), shows no detection up to a 5-sigma limiting magnitude of 20.74 (AB). We thus note this transient as a potential optical counterpart, and encourage further follow-up observations. 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/43974. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42094] Fermi GRB 260312B: Global MASTER-Net observations report
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43973 SUBJECT: Fermi GRB 260312B: Global MASTER-Net observations report DATE: 26/03/12 16:45:30 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260312B ( Fermi GBM team, GCN 43969) errorbox 24262 sec after notice time and 24340 sec after trigger time at 2026-03-12 16:32:26 UT, with upper limit up to 16.8 mag. Observations started at twilight. The observations began at zenith distance = 80 deg. The sun altitude is -15.4 deg. The galactic latitude b = -63 deg., longitude l = 154 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3182510 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 24370 | 2026-03-12 16:32:26 | MASTER-Kislovodsk | (01h 43m 41.60s , -02d 12m 39.7s) | C | 60 | 16.1 | 24472 | 2026-03-12 16:34:07 | MASTER-Kislovodsk | (01h 43m 29.55s , -00d 19m 40.6s) | C | 60 | 16.5 | 24577 | 2026-03-12 16:35:53 | MASTER-Kislovodsk | (01h 55m 57.24s , -04d 08m 01.4s) | C | 60 | 16.8 | 24677 | 2026-03-12 16:37:33 | MASTER-Kislovodsk | (01h 55m 42.13s , -02d 14m 03.2s) | C | 60 | 16.6 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43973. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42093] Fermi GRB 260311B: Global MASTER-Net observations report
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43972 SUBJECT: Fermi GRB 260311B: Global MASTER-Net observations report DATE: 26/03/12 12:32:31 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260311B ( Fermi GBM team, GCN 43964) errorbox 24516 sec after notice time and 24692 sec after trigger time at 2026-03-12 01:49:28 UT, with upper limit up to 15.6 mag. The observations began at zenith distance = 57 deg. The sun altitude is -18.9 deg. The galactic latitude b = 4 deg., longitude l = 32 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3181495 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 24723 | 2026-03-12 01:49:28 | MASTER-Kislovodsk | (19h 10m 01.93s , +04d 53m 01.1s) | C | 60 | 15.6 | 59805 | 2026-03-12 11:34:10 | MASTER- | (18h 18m 16.48s , +06d 44m 41.9s) | C | 60 | 17.4 | 59805 | 2026-03-12 11:34:10 | MASTER- | (18h 19m 31.23s , +06d 11m 34.9s) | C | 60 | 17.5 | 59876 | 2026-03-12 11:35:21 | MASTER- | (18h 26m 26.82s , +06d 44m 33.6s) | C | 60 | 17.2 | 59876 | 2026-03-12 11:35:21 | MASTER- | (18h 27m 41.28s , +06d 11m 25.0s) | C | 60 | 17.3 | 60391 | 2026-03-12 11:43:55 | MASTER- | (18h 18m 23.46s , +06d 44m 43.7s) | C | 60 | 17.2 | 60391 | 2026-03-12 11:43:55 | MASTER- | (18h 19m 38.47s , +06d 11m 36.0s) | C | 60 | 17.2 | 60478 | 2026-03-12 11:45:23 | MASTER- | (18h 26m 21.18s , +06d 44m 18.1s) | C | 60 | 17.3 | 60478 | 2026-03-12 11:45:23 | MASTER- | (18h 27m 36.03s , +06d 11m 09.5s) | C | 60 | 17.4 | 61508 | 2026-03-12 12:02:33 | MASTER- | (18h 18m 19.70s , +06d 44m 43.2s) | C | 60 | 17.5 | 61508 | 2026-03-12 12:02:33 | MASTER- | (18h 19m 35.99s , +06d 11m 38.1s) | C | 60 | 17.6 | 61579 | 2026-03-12 12:03:44 | MASTER- | (18h 26m 26.43s , +06d 45m 59.2s) | C | 60 | 17.5 | 61579 | 2026-03-12 12:03:44 | MASTER- | (18h 27m 42.44s , +06d 12m 52.6s) | C | 60 | 17.6 | 61657 | 2026-03-12 12:05:02 | MASTER- | (18h 02m 57.54s , +06d 46m 34.6s) | C | 60 | 17.4 | 61657 | 2026-03-12 12:05:02 | MASTER- | (18h 04m 14.17s , +06d 13m 30.5s) | C | 60 | 17.6 | 61729 | 2026-03-12 12:06:14 | MASTER- | (18h 12m 23.49s , +06d 12m 17.2s) | C | 60 | 17.5 | 61729 | 2026-03-12 12:06:14 | MASTER- | (18h 11m 06.96s , +06d 45m 21.9s) | C | 60 | 17.4 | 61810 | 2026-03-12 12:07:35 | MASTER- | (18h 23m 25.76s , +08d 38m 13.5s) | C | 60 | 17.5 | 61810 | 2026-03-12 12:07:35 | MASTER- | (18h 24m 42.43s , +08d 05m 07.3s) | C | 60 | 17.5 | 61890 | 2026-03-12 12:08:55 | MASTER- | (18h 31m 28.03s , +08d 39m 36.9s) | C | 60 | 16.7 | 61890 | 2026-03-12 12:08:55 | MASTER- | (18h 32m 44.52s , +08d 06m 30.1s) | C | 60 | 16.7 | 61964 | 2026-03-12 12:10:09 | MASTER- | (18h 08m 02.64s , +08d 40m 18.8s) | C | 60 | 17.5 | 61964 | 2026-03-12 12:10:09 | MASTER- | (18h 09m 19.69s , +08d 07m 14.2s) | C | 60 | 17.5 | 62053 | 2026-03-12 12:11:38 | MASTER- | (18h 16m 02.67s , +08d 39m 09.5s) | C | 60 | 17.8 | 62053 | 2026-03-12 12:11:38 | MASTER- | (18h 17m 19.59s , +08d 06m 04.4s) | C | 60 | 17.9 | 62137 | 2026-03-12 12:13:02 | MASTER- | (18h 19m 34.48s , +06d 13m 00.2s) | C | 60 | 17.5 | 62137 | 2026-03-12 12:13:02 | MASTER- | (18h 18m 17.96s , +06d 46m 05.6s) | C | 60 | 17.5 | 62213 | 2026-03-12 12:14:18 | MASTER- | (18h 27m 43.41s , +06d 11m 45.8s) | C | 60 | 17.6 | 62213 | 2026-03-12 12:14:18 | MASTER- | (18h 26m 27.07s , +06d 44m 51.9s) | C | 60 | 17.5 | 62289 | 2026-03-12 12:15:34 | MASTER- | (18h 04m 15.28s , +06d 11m 22.4s) | C | 60 | 17.8 | 62289 | 2026-03-12 12:15:34 | MASTER- | (18h 02m 58.43s , +06d 44m 26.1s) | C | 60 | 17.7 | 62361 | 2026-03-12 12:16:46 | MASTER- | (18h 11m 08.08s , +06d 44m 34.3s) | C | 60 | 17.5 | 62361 | 2026-03-12 12:16:46 | MASTER- | (18h 12m 24.83s , +06d 11m 29.9s) | C | 60 | 17.5 | 62435 | 2026-03-12 12:18:00 | MASTER- | (18h 24m 39.81s , +08d 06m 36.2s) | C | 60 | 17.6 | 62435 | 2026-03-12 12:18:00 | MASTER- | (18h 23m 22.92s , +08d 39m 41.6s) | C | 60 | 17.6 | 62534 | 2026-03-12 12:19:39 | MASTER- | (18h 31m 28.26s , +08d 38m 04.6s) | C | 60 | 16.7 | 62534 | 2026-03-12 12:19:39 | MASTER- | (18h 32m 45.03s , +08d 04m 58.7s) | C | 60 | 16.7 | 62607 | 2026-03-12 12:20:52 | MASTER- | (18h 09m 21.12s , +08d 06m 49.7s) | C | 60 | 17.5 | 62607 | 2026-03-12 12:20:52 | MASTER- | (18h 08m 03.80s , +08d 39m 53.7s) | C | 60 | 17.4 | 62679 | 2026-03-12 12:22:04 | MASTER- | (18h 17m 19.94s , +08d 05m 57.7s) | C | 60 | 18.0 | 62679 | 2026-03-12 12:22:04 | MASTER- | (18h 16m 02.75s , +08d 39m 01.9s) | C | 60 | 17.9 | 62750 | 2026-03-12 12:23:15 | MASTER- | (18h 19m 35.12s , +06d 12m 53.1s) | C | 60 | 17.8 | 62750 | 2026-03-12 12:23:15 | MASTER- | (18h 18m 18.36s , +06d 45m 57.6s) | C | 60 | 17.8 | 62825 | 2026-03-12 12:24:30 | MASTER- | (18h 27m 42.53s , +06d 11m 38.8s) | C | 60 | 17.7 | 62825 | 2026-03-12 12:24:30 | MASTER- | (18h 26m 25.94s , +06d 44m 44.0s) | C | 60 | 17.6 | 62898 | 2026-03-12 12:25:43 | MASTER- | (18h 04m 17.41s , +06d 11m 17.9s) | C | 60 | 17.9 | 62898 | 2026-03-12 12:25:43 | MASTER- | (18h 03m 00.33s , +06d 44m 20.9s) | C | 60 | 17.8 | 62970 | 2026-03-12 12:26:55 | MASTER- | (18h 12m 26.18s , +06d 11m 27.7s) | C | 60 | 17.6 | 62970 | 2026-03-12 12:26:55 | MASTER- | (18h 11m 09.22s , +06d 44m 31.3s) | C | 60 | 17.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43972. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42092] Swift BAT trigger 1500148: A solar flare
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43971 SUBJECT: Swift BAT trigger 1500148: A solar flare DATE: 26/03/12 10:45:18 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> P. A. Evans (U Leicester), C. Gronwall (PSU), R. Gupta (NASA GSFC), A. Y. Lien (U Tampa) and K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift Observatory Team: BAT trigger 1500148 is not a GRB, but was caused by a solar flare. Swift's automatic slews are currently disabled, so there will be no XRT or UVOT data for this trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/43971. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42091] GRB 260312B: BALROG localization (Fermi Trigger 795001611 / GRB 260312407)
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43970 SUBJECT: GRB 260312B: BALROG localization (Fermi Trigger 795001611 / GRB 260312407) DATE: 26/03/12 10:16:35 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 795001611 at 09:46:46 on 12 March 2026 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 26.3 deg Decl.(2000.0) = -8.3 deg The 1 sigma statistical error radius is 2.2 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB260312407/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB260312407/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB260312407/json View this GCN Circular online at https://gcn.nasa.gov/circulars/43970. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42090] GRB 260312B: Fermi GBM Final Real-time Localization
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43969 SUBJECT: GRB 260312B: Fermi GBM Final Real-time Localization DATE: 26/03/12 09:57:18 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 09:46:46 UT on 12 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260312B (trigger 795001611.054834 / 260312407). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 25.9, Dec = -3.9 (J2000 degrees, equivalent to J2000 01h 43m, -3d 53'), with a statistical uncertainty of 1.9 degrees. The angle from the Fermi LAT boresight is 67.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260312407/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260312407/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260312407/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43969. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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