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[vsnet-grb-info 42194] GRB 260310A: continued optical observation at Mondy
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44073 SUBJECT: GRB 260310A: continued optical observation at Mondy DATE: 26/03/21 22:21:34 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> N. Pankov (IKI), A. Volnova (IKI), E. Klunko (ISTP), A. S. Moskvitin (SAO RAS), O. Spiridonova (SAO RAS), A. Pozanenko (IKI) report on behalf of GRB IKI FuN. We continued observation the 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 on 2026-03-21. 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; Becerra et al., GCN 44059; Volnova et al., GCN 44060; Busmann et al., GCN 44061; Zheng t al., GCN 44065) is clearly detected in our images. Preliminary photometry is the following Date UT_start t_mid - T0, exp, mag, err, filter, UL(3sigma) days s 2026-03-21 16:35:57 11.48526 30*120 B 20.19 0.04 23.3 2026-03-21 16:04:50 11.46366 15*120 R 19.21 0.04 23.4 The photometry is based on the nearby calibrations stars of PS1 catalogue converted to B, R using the Lupton (2005) transformations. The magnitudes of the AT2026fgk are not corrected for Galactic extinctions. The light curve obtained from our observations and GCNs can be found in https://heaiki.ru/lvc/GRB260310A/GRB260310A_LC.png We can assume that the light curve becomes steeper 9 days after long lasting plateau phase View this GCN Circular online at https://gcn.nasa.gov/circulars/44073. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42193] Fermi GBM Sub-Threshold Detection of GRB 260321A
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44072 SUBJECT: Fermi GBM Sub-Threshold Detection of GRB 260321A DATE: 26/03/21 22:15:38 GMT FROM: rhamburg(a)usra.edu R. Hamburg (USRA) reports on behalf of the Fermi-GBM Team: SVOM/ECLAIRs detected GRB 260321A on 2026-03-21 at 18:12:08 UTC (GCN 44071). 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 10 s after the ECLAIRs best image SNR time of 2026-03-21T18:11:48. The Targeted Search candidate was found most significantly on the 8 s timescale using the "normal" spectral template (i.e., Band function with Epeak = 230 keV, alpha = -1.0, beta = -2.3) and has a false alarm rate of 3.7e-04 Hz. The Fermi-MET of this transient is 795809523.353 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/44072. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42192] GRB 260321A: SVOM detection of a burst
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44071 SUBJECT: GRB 260321A: SVOM detection of a burst DATE: 26/03/21 18:39:15 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, O. Godet (IRAP) report on behalf of the SVOM mission team: At 2026-03-21T18:12:08 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260321A (SVOM burst-id sb26032123). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was only detected by the Image Trigger (IMT), which produced a sequence of 2 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 9.37 in the [8-120] keV energy band over a time window of 40.96 seconds starting at 2026-03-21T18:11:48. The localization of the best alert is R.A., Dec. 219.574, 31.674 degrees: R.A. (J2000) = 14h38m17.65s Dec. (J2000) = 31d40m28.18s with a 90% confidence level (C.L.) radius of 8.45 arcmin (including systematic error of 2 arcmin added in quadrature). This burst also triggered SVOM/GRM at 2026-03-21T18:12:08 with an SNR of 10.9. The SVOM/GRM light curve showed a multiple peak structure with a T90 duration of about 113.02 -18.24 / +74.15 (8-1100 keV). 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 Marius Brunet: mbrunet(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/44071. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42191] EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44070 SUBJECT: EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle DATE: 26/03/21 17:18:54 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> M.-H. Lee, A. Aryan, T.-W. Chen, W.-J. Hou (all NCU), S. Yang (HNAS), S. J. Smartt, J. Gillanders (both Oxford), A. K. H. Kong (NTHU), Y. J. Yang (NYUAD), Y.-H. Lee, A. Sankar.K, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, C.-S. Lin H.-C. Lin, H.-Y. Hsiao, J.-K. Guo (all NCU), Z. N. Wang, D. C. Qiang, L. L. Fan (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP260321a (Huang et al., GCN 44068 using the 1m LOT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first LOT epoch of observations started at 13:38 UTC on the 21st of March 2026 (MJD 61120.568), 1.13 hr after the EP-WXT trigger. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. In the difference image, we detected an obvious residual at RA, DEC = 09:59:42.82, 00:25:05.84. We noticed that this position coincides with a stellar source that sits close on top of a resolved galaxy detected in SDSS, Pan-STARRS1 and Legacy Surveys (SDSS J095942.88+002506.2). The stellar source has varying magnitudes in different catalogs (PS1 r = 20.42 +/- 0.25, SDSS r = 21.07 +/- 0.05, DESI r = 19.07). This is likely an unrelated variable star. Moreover, we used AutoPhOT to perform PSF photometry at the residual's position. The details of the observations and the measured magnitude (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass LOT | r | 61120.568 | 1.13 | 300 * 6 | 20.97 +/- 0.04 | 1".02 | 1.09 Our 3-sigma upper limit for the observed field is r = 23.1 mag using the SDSS catalogue as the reference. The galaxy SDSS J095942.88+002506.2 is at z = 0.0343, as measured in 2dF and in the DESI Legacy Survey DR1 spectroscopic catalogue (TARGETID: 39627799320858502) lies within the EP FXT localisation region. If EP260321 is associated with this galaxy, then our detection limits imply there is no new source brighter than an absolute magnitude of M ~ -12.6 mag at t-t0 = 1.13 hours after the FXT trigger. A supernova or kilonova would still be rapidly rising in this phase; further observations are encouraged. The presented magnitude is calibrated using the field stars from the ATLAS-RefCat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105) and is not corrected for the expected Galactic foreground extinction of A_r = 0.06 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 can be found 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/44070. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42190] EP260321a: Global MASTER-Net observations report
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44069 SUBJECT: EP260321a: Global MASTER-Net observations report DATE: 26/03/21 13:54:25 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Tunka robotic telescope [1] located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the EP260321a ( EP Team et al., GCN 44068) errorbox 194 sec after notice time and 2105 sec after trigger time at 2026-03-21 13:05:23 UT, with upper limit up to 19.1 mag. Observations started at twilight. The observations began at zenith distance = 56 deg. The sun altitude is -16.9 deg. The galactic latitude b = 41 deg., longitude l = 239 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3200651 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 2135 | 2026-03-21 13:05:23 | MASTER-Tunka | (09h 57m 47.48s , +00d 56m 51.7s) | C | 60 | 18.8 | 2135 | 2026-03-21 13:05:23 | MASTER-Tunka | (09h 57m 34.12s , +01d 01m 05.4s) | C | 60 | 19.0 | 2208 | 2026-03-21 13:06:36 | MASTER-Tunka | (09h 57m 50.16s , +00d 58m 39.4s) | C | 60 | 18.8 | 2208 | 2026-03-21 13:06:36 | MASTER-Tunka | (09h 57m 36.78s , +01d 02m 53.3s) | C | 60 | 19.1 | 2283 | 2026-03-21 13:07:50 | MASTER-Tunka | (09h 57m 44.76s , +00d 57m 41.4s) | C | 60 | 18.9 | 2283 | 2026-03-21 13:07:50 | MASTER-Tunka | (09h 57m 31.35s , +01d 01m 55.6s) | C | 60 | 19.1 | 2354 | 2026-03-21 13:09:02 | MASTER-Tunka | (09h 57m 45.04s , +00d 58m 40.3s) | C | 60 | 18.8 | 2354 | 2026-03-21 13:09:02 | MASTER-Tunka | (09h 57m 31.61s , +01d 02m 54.6s) | C | 60 | 19.0 | 2429 | 2026-03-21 13:10:17 | MASTER-Tunka | (09h 57m 50.55s , +00d 57m 39.6s) | C | 60 | 18.8 | 2429 | 2026-03-21 13:10:17 | MASTER-Tunka | (09h 57m 37.10s , +01d 01m 53.7s) | C | 60 | 19.0 | 2502 | 2026-03-21 13:11:30 | MASTER-Tunka | (09h 57m 45.69s , +00d 56m 38.6s) | C | 60 | 18.9 | 2502 | 2026-03-21 13:11:30 | MASTER-Tunka | (09h 57m 32.22s , +01d 00m 52.6s) | C | 60 | 19.1 | 2575 | 2026-03-21 13:12:42 | MASTER-Tunka | (09h 57m 37.50s , +01d 01m 04.8s) | C | 60 | 19.1 | 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/44069. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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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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