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[vsnet-grb-info 42287] Konus-Wind detection of GRB 260316B
by GCN Circulars 31 Mar '26

31 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44166 SUBJECT: Konus-Wind detection of GRB 260316B DATE: 26/03/31 13:32:31 GMT FROM: Valentina Panteleeva at Ioffe Institute <panteleevav228(a)gmail.com> V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260316B (Fermi-GBM detection: The Fermi GBM team, GCN 44031; AstroSat CZTI detection: Harsha et al., GCN 44035, SVOM/GRM detection: Wang et al., GCN 44039, GECAM-B detection: Wang et al., GCN 44040, CALET-GBM detection: Tamura et al., GCN 44100, IPN triangulation: Kozyrev et al., GCN 44111) triggered Konus-Wind at T0=61972.457 s UT (17:12:52.457). The burst light curve shows a single pulse which starts at ~T0-0.9 s and has a total duration of ~2.5 s. The emission is seen up to ~5 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260316_T61972/ As observed by Konus-Wind, the burst had the total fluence of 2.66(-0.45,+0.56)x10^-6 erg/cm2, and the 64-ms peak flux, measured from T0+0.230 s, of 2.87(-0.74,+0.85)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.24(-0.65,+0.76), the high energy photon index beta = -2.64(-7.36,+0.34), the peak energy Ep = 123(-22,+58) keV (chi2 = 64/77 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/44166. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42286] Konus-Wind detection of GRB 260316B
by GCN Circulars 31 Mar '26

31 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44165 SUBJECT: Konus-Wind detection of GRB 260316B DATE: 26/03/31 13:32:29 GMT FROM: Valentina Panteleeva at Ioffe Institute <panteleevav228(a)gmail.com> V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260316B (Fermi-GBM detection: The Fermi GBM team, GCN 44031; AstroSat CZTI detection: Harsha et al., GCN 44035, SVOM/GRM detection: Wang et al., GCN 44039, GECAM-B detection: Wang et al., GCN 44040, CALET-GBM detection: Tamura et al., GCN 44100, IPN triangulation: Kozyrev et al., GCN 44111) triggered Konus-Wind at T0=61972.457 s UT (17:12:52.457). The burst light curve shows a single pulse which starts at ~T0-0.9 s and has a total duration of ~2.5 s. The emission is seen up to ~5 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260316_T61972/ As observed by Konus-Wind, the burst had the total fluence of 2.66(-0.45,+0.56)x10^-6 erg/cm2, and the 64-ms peak flux, measured from T0+0.230 s, of 2.87(-0.74,+0.85)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.24(-0.65,+0.76), the high energy photon index beta = -2.64(-7.36,+0.34), the peak energy Ep = 123(-22,+58) keV (chi2 = 64/77 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/44165. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42285] GRB 260321A: SVOM/ECLAIRs refined analysis
by GCN Circulars 31 Mar '26

31 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44164 SUBJECT: GRB 260321A: SVOM/ECLAIRs refined analysis DATE: 26/03/31 12:06:20 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, O.Godet, F. Triot, J.-L. Atteia (IRAP), report on behalf of the SVOM/ECLAIRs team Using the event-by-event data downloaded through the X-band ground station, we report further analysis of SVOM/ECLAIRs observations of GRB 260321A (SVOM burst-id sb26032123 – GCN 44071, trigger time T0 = 2026-03-21T18:12:08 UTC), which was also detected by Fermi/GBM as a sub-threshold event (GCN 44072). The burst that triggered ECLAIRs onboard shows a single peak lightcurve, followed by a featureless emission tail. The burst duration is estimated to be around 57 s in the 4-50 keV energy band through imaging. The ECLAIRs light curve can be found here: https://docs.google.com/document/d/1aA9Ams6NNpz7RKQksAyu6mulcFsYo2OPOXFnpyy… The time-averaged spectrum from T0-16 s to T0+34.92 s in the 5-120 keV energy range is best fitted by a broken power-law model with a first photon index of -0.65 +0.32/-0.25, a second photon index of -2.71 +0.77/-1.59 and a break energy of 33.4 +4.6/-4.7 keV. With this model, the 4-120 keV fluence is (4.9 +0.6/-3.6)e-7 erg/cm^2 and the 4-120 keV photon flux is 0.23 +0.20/0.17 ph/cm^2/s. This GRB shows some spectral evolution. The spectrum from T0-16s s to T0 in the 5-120 keV energy range is best fitted by a power-law model with a photon index of -1.06 +/-0.13. With this model, the 4-120 keV flux is (2.3 +0.1/-0.6)e-8 erg/cm²/s. The spectrum from T0 to T0+34.92 s in the 5-120 keV energy range is well fitted using a broken power-law model, fixing the first photon index to -1 and the second to -3, with a break energy of 35.7 +12.6/-10.4 keV. With this model, the 4-120 keV flux is (0.7 +/-0.1)e-9 erg/cm²/s. The position of GRB 260321A in the Amati relation diagram is compatible with those of Type-II GRBs if it is at a redshift larger than 3. The non detection of an optical afterglow even with early deep observations (SVOM/Colibri upper limit, GCN 44078 & GCN 44102 and SVOM/VT upper limit GCN 44080) may also favor a high redshift origin for this burst. All the quoted errors are at the 68% confidence level. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Marius Brunet (IRAP) (marius.brunet at utoulouse.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/44164. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42284] EP260329b: J-band upper limits with WINTER
by GCN Circulars 31 Mar '26

31 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44163 SUBJECT: EP260329b: J-band upper limits with WINTER DATE: 26/03/31 00:28:16 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Caltech/Carnegie), Tomas Ahumada (NOIRLab), Benjamin Schneider (LAM), Robert Stein (UMD), Viraj Karambelkar (Columbia), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of EP260329b (Song et al., GCN 44142, GCN 44155) in the near-infrared J band with 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 2026-03-30T04:09:30 UTC in the J band (~17.6 hr after the GRB trigger), consisting of 15 x 120 s exposures. 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 do not detect a source at the optical counterpart location (Li et al., GCN 44139; Eyles-Ferris et al., GCN 44144; Magnani et al., GCN 44146; Aryan et al., GCN 44147; Lipunov et al., GCN 44150). We obtain the following 5-sigma upper limit: J = 19.3 mag (AB). 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/44163. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42283] EP260329a: J-band upper limit with WINTER
by GCN Circulars 31 Mar '26

31 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44162 SUBJECT: EP260329a: J-band upper limit with WINTER DATE: 26/03/31 00:27:44 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Caltech/Carnegie), Benjamin Schneider (LAM), Tomas Ahumada (NOIRLab), Robert Stein (UMD), Viraj Karambelkar (Columbia), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of EP260329a (Yang et al., GCN 44141) in the near-infrared J band with 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 2026-03-29T11:11:03 UTC in the J band (~7.7 hr after the GRB trigger), consisting of 15 x 120 s exposures. 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 do not detect a source at the optical counterpart location (Sankar et al., GCN 44145; He et al., GCN 44152; Yang et al., GCN 44153; Angulo et al., GCN 44154). We obtain the following 5-sigma upper limit: J = 18.0 mag (AB). 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/44162. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42282] GRB 260330A: Glowbug gamma-ray detection
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44161 SUBJECT: GRB 260330A: Glowbug gamma-ray detection DATE: 26/03/30 21:27:51 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, confirms the detection of GRB 260330A, which was detected by Fermi/GBM (GCN 44151). The burst onset is at 2026-03-30 03:40:18.4 with a burst duration of ~16s. The lightcurve comprises an initial faint peak at ~T0+0.2s, followed by bright multi-peaked structures from ~T0+3s to +6s and ~T0+9s to +15.5s. 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/44161. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42281] GRB 260310A: VLA Multi-frequency Radio Observations
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44160 SUBJECT: GRB 260310A: VLA Multi-frequency Radio Observations DATE: 26/03/30 20:08:21 GMT FROM: Daniel Perley at Liverpool JMU <d.a.perley(a)ljmu.ac.uk> D. A. Perley (LJMU), G. Schroeder (Cornell), and T. Laskar (Utah) report on behalf of a larger collaboration: The Karl G. Jansky Very Large Array observed the location of the afterglow (Hinds et al., TNS AstroNote 2026-65; Konno et al., GCN 43974) associated with GRB 260310A (Fermi GBM Team, GCN 43951; Hamburg & Meegan, GCN 43975) using all available receivers from S-band to Q-band, providing nearly continuous spectral coverage from 2 to 50 GHz. Observations were carried out on UT 2026-03-27 between 07:45 and 11:06 UT, approximately 17.2 days after the GRB. Consistent with previous reports (Rhodes et al., GCN 44005; Giarratana et al., GCN 44045; Ho et al., GCN 44057; Ho et al., GCN 44134) we detect very strong radio emission from the afterglow. Preliminary flux densities are: | freq(GHz) | flux(mJy) | |-----------|----------------| | 3 | 2.90 +/- 0.04 | | 6 | 7.52 +/- 0.05 | | 10 | 11.11 +/- 0.11 | | 15 | 11.73 +/- 0.16 | | 33 | 9.58 +/- 0.39 | | 45 | 7.98 +/- 0.27 | This indicates that the afterglow has brightened at low frequencies since the observations of Giarratana et al. and Rhodes et al. at ~4 days post-GRB, and that the peak of the f_nu spectral energy distribution during our observations was at approximately 15 GHz. We thank the NRAO for rapidly approving our DDT request for a public multifrequency campaign on this exceptional GRB, and Heidi Medlin for assistance with checking the SBs. Further observations are planned. View this GCN Circular online at https://gcn.nasa.gov/circulars/44160. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42280] Fermi GBM Sub-Threshold Detection of GRB 260330B
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44159 SUBJECT: Fermi GBM Sub-Threshold Detection of GRB 260330B DATE: 26/03/30 19:48:13 GMT FROM: atrigg2(a)lsu.edu A.C. Trigg (NPP ORAU, NASA MSFC) reports on behalf of the Fermi-GBM Team: SVOM/ECLAIRs detected GRB 260330B on 2026-03-30 at 14:19:57 UTC (GCN 44157). There was no Fermi-GBM onboard trigger around this event time. An automated, blind search for gamma-ray bursts below the onboard triggering threshold in Fermi-GBM identified no candidates. The GBM Targeted Search [1], the most sensitive coherent search for GRB-like signals in GBM, identified a transient approximately 16 s after the ECLAIRs best image SNR time of 2026-03-30T14:19:31. The Targeted Search candidate was found most significantly on the 32 s timescale using the "soft" spectral template (i.e., Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) and has a false alarm rate of 1.0-04 Hz. The Fermi-MET of this transient is 796573176.806 s. The Targeted Search localization is spatially consistent with the ECLAIRs location. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/44159. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42279] GRB 260330B: LCO optical upper limits
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44158 SUBJECT: GRB 260330B: LCO optical upper limits DATE: 26/03/30 18:58:32 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> D. Turpin (CEA/Irfu), A. Saccardi (CEA/Irfu), G. X. Lan (IRAP), S. Guillot (IRAP), report on behalf of the SVOM mission team: We observed the field of GRB 260330B detected by SVOM (Lan et al., GCN 44157) with the LCO 1m telescope at Siding Spring Observatory equipped with the Sinistro instrument. Our observation started on 2026-03-30 at 17:05:41 UT (about 2.76 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. In the stacked image, we do not detect any new source within the SVOM/ECLAIRs error box. We measure the following upper limit calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction: r > 20.4 AB (5-sigma, mid-time 2.85 hr after the trigger); z > 19.2 AB (5-sigma, mid-time 2.86 hr after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/44158. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42278] GRB 260330B: SVOM detection of a burst
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44157 SUBJECT: GRB 260330B: SVOM detection of a burst DATE: 26/03/30 14:50:52 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> G. X. Lan, S. Guillot, H. Yang, O. Godet (IRAP), report on behalf of the SVOM mission team: At 2026-03-30T14:19:57 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260330B (SVOM burst-id sb26033003). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 9 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 12.13 in the [5-20] keV energy band over a time window of 40.96 seconds starting at 2026-03-30T14:19:31. The localization of the best alert is R.A., Dec. 252.555, 36.862 degrees: R.A. (J2000) = 16h50m13s Dec. (J2000) = 36d51m44s with a 90% confidence level (C.L.) radius of 6.66 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve showed multiple broad peak structures with a T90 duration of about 20.844 (-3.025 / +7.55) s. This burst was also detected by SVOM/GRM with a significance of 9.10. SVOM slewed to the burst. No X-ray observation could be performed by SVOM/MXT for the time being. No optical observation could be performed by SVOM/VT for the time being. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Guangxuan Lan: glan(a)irap.omp.eu. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44157. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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