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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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