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[vsnet-grb-info 42490] GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44368 SUBJECT: GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115 DATE: 26/04/21 06:41:33 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> B. Schneider (LAM), A. Saccardi (CEA/Irfu), N. Habeeb (Leicester), R. Brivio (INAF/OAB), A. L. Thakur (INAF/IAPS), D. B. Malesani (DAWN/NBI and Radboud), report on behalf of the Stargate collaboration: We observed the optical counterpart (He et al., GCN 44363; Sanchez-Alvarez, GCN 44364; Turpin et al., GCN 44365; Wu et al., GCN 44366) of the SVOM and Fermi GRB 260421B (Zhao et al., GCN 44362; Fermi GBM Team, GCN 44360) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-25000 AA, and consist of 4 exposures of 600 s each. The observation mid time was 05:39 UT on 2026 April 21 (1.42 hr after the SVOM/ECLAIRs trigger). In a 5-s acquisition image (taken 61 min after the SVOM/ECLAIRs trigger), the afterglow is detected with a magnitude r = 20.43 +/- 0.05 AB, calibrated against the single Pan-STARRS object lying in our field of view, and not corrected for Galactic extinction. In a preliminary reduction of the spectra, we detect a continuum over the entire wavelength range. At the blue edge of the spectrum, we identify a broad trough at around 3786 AA, likely due to H I Lyman-alpha. Multiple absorption lines are also detected, which we interpret as due to, among others, S II, Si II, O I, Si II*, C II, C II*, Si IV, C IV, Fe II, Fe II*, Mg II, all at a common redshift z = 2.115. We consider this to be the redshift of GRB 260421B. We acknowledge the excellent expert support from the observing staff in Paranal, in particular Francisco Caceres and Matias Jones. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495) We thank the COLIBRÍ (FM-GFT) team for alerting us of the afterglow prior to their GCN release. View this GCN Circular online at https://gcn.nasa.gov/circulars/44368. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42489] Fermi GRB 260421B: Global MASTER-Net observations report
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44367 SUBJECT: Fermi GRB 260421B: Global MASTER-Net observations report DATE: 26/04/21 05:45:38 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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260421B ( Fermi GBM team, GCN 44360) errorbox 93 sec after notice time and 126 sec after trigger time at 2026-04-21 04:15:27 UT, with upper limit up to 19.9 mag. The observations began at zenith distance = 56 deg. The sun altitude is -28.9 deg. MASTER-OAFA robotic telescope located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 260421B errorbox 867 sec after notice time and 900 sec after trigger time at 2026-04-21 04:28:21 UT, with upper limit up to 20.2 mag. The observations began at zenith distance = 21 deg. The sun altitude is -70.7 deg. The galactic latitude b = 45 deg., longitude l = 298 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3262990 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 142 | 2026-04-21 04:15:27 | MASTER-OAGH | (12h 53m 10.93s , -17d 20m 23.6s) | C | 30 | 18.4 | 177 | 2026-04-21 04:15:27 | MASTER-OAGH | (12h 53m 10.93s , -17d 20m 23.5s) | C | 100 | 19.1 | Coadd 181 | 2026-04-21 04:16:07 | MASTER-OAGH | (12h 53m 17.82s , -17d 20m 17.3s) | C | 30 | 18.5 | 226 | 2026-04-21 04:16:47 | MASTER-OAGH | (12h 53m 13.89s , -17d 18m 44.5s) | C | 40 | 18.4 | 282 | 2026-04-21 04:17:37 | MASTER-OAGH | (12h 53m 13.81s , -17d 20m 10.6s) | C | 50 | 18.7 | 352 | 2026-04-21 04:17:37 | MASTER-OAGH | (12h 53m 13.81s , -17d 20m 10.6s) | C | 190 | 19.7 | Coadd 347 | 2026-04-21 04:18:38 | MASTER-OAGH | (12h 53m 17.74s , -17d 19m 02.7s) | C | 60 | 18.8 | 427 | 2026-04-21 04:19:48 | MASTER-OAGH | (12h 53m 11.54s , -17d 19m 39.5s) | C | 80 | 19.2 | 538 | 2026-04-21 04:21:28 | MASTER-OAGH | (12h 35m 06.04s , -17d 47m 57.6s) | C | 100 | 19.2 | 538 | 2026-04-21 04:21:28 | MASTER-OAGH | (12h 36m 24.29s , -18d 21m 51.5s) | C | 100 | 19.4 | 980 | 2026-04-21 04:28:11 | MASTER-OAGH | (12h 39m 45.91s , -17d 46m 54.8s) | P- | 180 | 17.5 | 980 | 2026-04-21 04:28:11 | MASTER-OAGH | (12h 41m 04.22s , -18d 20m 54.9s) | P| | 180 | 17.7 | 1160 | 2026-04-21 04:28:11 | MASTER-OAGH | (12h 41m 04.22s , -18d 20m 54.8s) | P| | 540 | 18.8 | Coadd 930 | 2026-04-21 04:28:21 | MASTER-OAFA | (12h 40m 14.08s , -17d 24m 25.2s) | C | 60 | 20.0 | 996 | 2026-04-21 04:29:26 | MASTER-OAFA | (12h 40m 14.11s , -17d 24m 23.6s) | C | 60 | 20.1 | 1061 | 2026-04-21 04:30:32 | MASTER-OAFA | (12h 40m 14.15s , -17d 24m 22.0s) | C | 60 | 20.1 | 1170 | 2026-04-21 04:31:21 | MASTER-OAGH | (12h 39m 52.24s , -17d 46m 46.8s) | P- | 180 | 17.7 | 1170 | 2026-04-21 04:31:21 | MASTER-OAGH | (12h 41m 10.67s , -18d 20m 47.4s) | P| | 180 | 18.1 | 1127 | 2026-04-21 04:31:38 | MASTER-OAFA | (12h 40m 14.20s , -17d 24m 20.9s) | C | 60 | 20.2 | 1193 | 2026-04-21 04:32:44 | MASTER-OAFA | (12h 40m 14.23s , -17d 24m 19.6s) | C | 60 | 20.1 | 1259 | 2026-04-21 04:33:49 | MASTER-OAFA | (12h 40m 14.26s , -17d 24m 18.2s) | C | 60 | 20.1 | 1361 | 2026-04-21 04:34:31 | MASTER-OAGH | (12h 39m 49.24s , -17d 45m 09.3s) | P- | 180 | 17.7 | 1361 | 2026-04-21 04:34:31 | MASTER-OAGH | (12h 41m 07.78s , -18d 19m 10.2s) | P| | 180 | 18.3 | 1325 | 2026-04-21 04:34:56 | MASTER-OAFA | (12h 40m 14.30s , -17d 24m 16.6s) | C | 60 | 20.0 | 1391 | 2026-04-21 04:36:01 | MASTER-OAFA | (12h 40m 14.36s , -17d 24m 15.7s) | C | 60 | 20.2 | 1456 | 2026-04-21 04:37:07 | MASTER-OAFA | (12h 40m 14.39s , -17d 24m 14.3s) | C | 60 | 20.1 | 1552 | 2026-04-21 04:37:43 | MASTER-OAGH | (12h 39m 49.10s , -17d 46m 59.8s) | P- | 180 | 17.9 | 1552 | 2026-04-21 04:37:43 | MASTER-OAGH | (12h 41m 07.75s , -18d 21m 00.3s) | P| | 180 | 18.3 | 1522 | 2026-04-21 04:38:13 | MASTER-OAFA | (12h 40m 14.44s , -17d 24m 13.3s) | C | 60 | 20.2 | 1588 | 2026-04-21 04:39:18 | MASTER-OAFA | (12h 40m 14.44s , -17d 24m 12.1s) | C | 60 | 20.1 | 1653 | 2026-04-21 04:40:24 | MASTER-OAFA | (12h 40m 14.48s , -17d 24m 10.8s) | C | 60 | 20.1 | 1742 | 2026-04-21 04:40:53 | MASTER-OAGH | (12h 39m 51.19s , -17d 45m 34.9s) | P- | 180 | 17.7 | 1742 | 2026-04-21 04:40:53 | MASTER-OAGH | (12h 41m 09.87s , -18d 19m 35.1s) | P| | 180 | 18.4 | 1720 | 2026-04-21 04:41:30 | MASTER-OAFA | (12h 40m 14.54s , -17d 24m 09.9s) | C | 60 | 20.1 | 1785 | 2026-04-21 04:42:36 | MASTER-OAFA | (12h 40m 14.54s , -17d 24m 08.9s) | C | 60 | 20.1 | 1850 | 2026-04-21 04:43:41 | MASTER-OAFA | (12h 40m 14.57s , -17d 24m 07.9s) | C | 60 | 20.0 | 1874 | 2026-04-21 04:44:05 | MASTER-OAGH | (12h 34m 22.11s , -17d 48m 09.2s) | C | 60 | 19.5 | 1874 | 2026-04-21 04:44:05 | MASTER-OAGH | (12h 35m 41.12s , -18d 22m 06.8s) | C | 60 | 19.7 | 1917 | 2026-04-21 04:44:48 | MASTER-OAFA | (12h 40m 14.60s , -17d 24m 07.3s) | C | 60 | 20.1 | 1946 | 2026-04-21 04:45:17 | MASTER-OAGH | (12h 25m 58.60s , -17d 47m 08.9s) | C | 60 | 19.3 | 1946 | 2026-04-21 04:45:17 | MASTER-OAGH | (12h 27m 17.78s , -18d 21m 05.4s) | C | 60 | 19.7 | 1982 | 2026-04-21 04:45:53 | MASTER-OAFA | (12h 40m 14.65s , -17d 24m 05.9s) | C | 60 | 20.1 | 2047 | 2026-04-21 04:46:58 | MASTER-OAFA | (12h 40m 14.66s , -17d 24m 04.9s) | C | 60 | 20.1 | 2113 | 2026-04-21 04:48:04 | MASTER-OAFA | (12h 40m 14.68s , -17d 24m 03.9s) | C | 60 | 20.1 | 2179 | 2026-04-21 04:49:09 | MASTER-OAFA | (12h 40m 14.72s , -17d 24m 02.9s) | C | 60 | 20.2 | 2245 | 2026-04-21 04:50:15 | MASTER-OAFA | (12h 40m 14.76s , -17d 24m 02.1s) | C | 60 | 20.2 | 2311 | 2026-04-21 04:51:22 | MASTER-OAFA | (12h 40m 14.77s , -17d 24m 00.8s) | C | 60 | 20.1 | 2376 | 2026-04-21 04:52:27 | MASTER-OAFA | (12h 40m 14.82s , -17d 24m 00.2s) | C | 60 | 20.2 | 2442 | 2026-04-21 04:53:32 | MASTER-OAFA | (12h 40m 14.86s , -17d 23m 59.2s) | C | 60 | 20.2 | 2474 | 2026-04-21 04:54:05 | MASTER-OAGH | (12h 34m 21.59s , -17d 48m 11.5s) | C | 60 | 19.4 | 2474 | 2026-04-21 04:54:05 | MASTER-OAGH | (12h 35m 40.80s , -18d 22m 07.1s) | C | 60 | 19.8 | 2508 | 2026-04-21 04:54:39 | MASTER-OAFA | (12h 40m 14.86s , -17d 23m 58.4s) | C | 60 | 20.1 | 2546 | 2026-04-21 04:55:17 | MASTER-OAGH | (12h 25m 58.36s , -17d 49m 11.4s) | C | 60 | 19.5 | 2546 | 2026-04-21 04:55:17 | MASTER-OAGH | (12h 27m 17.73s , -18d 23m 06.0s) | C | 60 | 19.7 | 2574 | 2026-04-21 04:55:44 | MASTER-OAFA | (12h 40m 14.88s , -17d 23m 57.6s) | C | 60 | 20.0 | 2640 | 2026-04-21 04:56:50 | MASTER-OAFA | (12h 40m 14.94s , -17d 23m 56.9s) | C | 60 | 20.1 | 2706 | 2026-04-21 04:57:57 | MASTER-OAFA | (12h 40m 14.96s , -17d 23m 55.9s) | C | 60 | 20.0 | 2771 | 2026-04-21 04:59:02 | MASTER-OAFA | (12h 40m 15.00s , -17d 23m 54.7s) | C | 60 | 20.0 | 2837 | 2026-04-21 05:00:08 | MASTER-OAFA | (12h 40m 15.01s , -17d 23m 53.9s) | C | 60 | 19.9 | 2903 | 2026-04-21 05:01:14 | MASTER-OAGH | (12h 34m 23.48s , -19d 42m 11.3s) | C | 60 | 18.8 | 2903 | 2026-04-21 05:01:14 | MASTER-OAGH | (12h 35m 43.55s , -20d 16m 06.9s) | C | 60 | 19.0 | 2903 | 2026-04-21 05:01:14 | MASTER-OAFA | (12h 40m 15.04s , -17d 23m 53.2s) | C | 60 | 20.0 | 2968 | 2026-04-21 05:02:19 | MASTER-OAFA | (12h 40m 15.06s , -17d 23m 52.6s) | C | 60 | 20.0 | 2974 | 2026-04-21 05:02:25 | MASTER-OAGH | (12h 42m 52.05s , -19d 41m 12.6s) | C | 60 | 18.6 | 2974 | 2026-04-21 05:02:25 | MASTER-OAGH | (12h 44m 12.00s , -20d 15m 09.4s) | C | 60 | 19.1 | 3034 | 2026-04-21 05:03:25 | MASTER-OAFA | (12h 40m 15.10s , -17d 23m 51.8s) | C | 60 | 20.0 | 3100 | 2026-04-21 05:04:31 | MASTER-OAFA | (12h 40m 15.14s , -17d 23m 51.1s) | C | 60 | 19.9 | 3106 | 2026-04-21 05:04:37 | MASTER-OAGH | (12h 34m 20.33s , -17d 47m 13.7s) | C | 60 | 19.1 | 3106 | 2026-04-21 05:04:37 | MASTER-OAGH | (12h 35m 39.73s , -18d 21m 08.6s) | C | 60 | 19.2 | 3166 | 2026-04-21 05:05:37 | MASTER-OAFA | (12h 40m 15.18s , -17d 23m 50.7s) | C | 60 | 20.0 | 3177 | 2026-04-21 05:05:47 | MASTER-OAGH | (12h 26m 02.37s , -17d 48m 11.9s) | C | 60 | 19.3 | 3177 | 2026-04-21 05:05:47 | MASTER-OAGH | (12h 27m 21.94s , -18d 22m 05.5s) | C | 60 | 19.6 | 3232 | 2026-04-21 05:06:42 | MASTER-OAFA | (12h 40m 15.19s , -17d 23m 50.1s) | C | 60 | 20.0 | 3298 | 2026-04-21 05:07:49 | MASTER-OAFA | (12h 40m 15.22s , -17d 23m 49.4s) | C | 60 | 20.1 | 3307 | 2026-04-21 05:07:58 | MASTER-OAGH | (12h 34m 24.99s , -15d 54m 14.3s) | C | 60 | 19.5 | 3307 | 2026-04-21 05:07:58 | MASTER-OAGH | (12h 35m 43.97s , -16d 28m 07.6s) | C | 60 | 19.6 | 3363 | 2026-04-21 05:08:54 | MASTER-OAFA | (12h 40m 15.24s , -17d 23m 48.3s) | C | 60 | 20.0 | 3378 | 2026-04-21 05:09:08 | MASTER-OAGH | (12h 42m 36.90s , -15d 55m 16.1s) | C | 60 | 19.3 | 3378 | 2026-04-21 05:09:08 | MASTER-OAGH | (12h 43m 55.82s , -16d 29m 09.9s) | C | 60 | 19.6 | 3429 | 2026-04-21 05:09:59 | MASTER-OAFA | (12h 40m 15.26s , -17d 23m 47.3s) | C | 60 | 20.0 | 3495 | 2026-04-21 05:11:05 | MASTER-OAFA | (12h 40m 15.29s , -17d 23m 46.6s) | C | 60 | 20.0 | 3509 | 2026-04-21 05:11:20 | MASTER-OAGH | (12h 34m 22.74s , -19d 41m 12.5s) | C | 60 | 19.6 | 3509 | 2026-04-21 05:11:20 | MASTER-OAGH | (12h 35m 43.08s , -20d 15m 06.9s) | C | 60 | 19.9 | 3560 | 2026-04-21 05:12:11 | MASTER-OAFA | (12h 40m 15.29s , -17d 23m 46.2s) | C | 60 | 20.0 | 3581 | 2026-04-21 05:12:32 | MASTER-OAGH | (12h 42m 57.79s , -19d 42m 14.3s) | C | 60 | 19.6 | 3581 | 2026-04-21 05:12:32 | MASTER-OAGH | (12h 44m 18.06s , -20d 16m 09.5s) | C | 60 | 19.7 | 3626 | 2026-04-21 05:13:17 | MASTER-OAFA | (12h 40m 15.31s , -17d 23m 45.6s) | C | 60 | 20.0 | 3692 | 2026-04-21 05:14:23 | MASTER-OAFA | (12h 40m 15.34s , -17d 23m 45.0s) | C | 60 | 20.0 | 3719 | 2026-04-21 05:14:50 | MASTER-OAGH | (12h 34m 21.06s , -17d 47m 14.4s) | C | 60 | 19.6 | 3719 | 2026-04-21 05:14:50 | MASTER-OAGH | (12h 35m 40.72s , -18d 21m 07.3s) | C | 60 | 19.9 | 3758 | 2026-04-21 05:15:29 | MASTER-OAFA | (12h 40m 15.36s , -17d 23m 44.7s) | C | 60 | 20.1 | 3791 | 2026-04-21 05:16:02 | MASTER-OAGH | (12h 26m 01.87s , -17d 48m 12.2s) | C | 60 | 19.3 | 3791 | 2026-04-21 05:16:02 | MASTER-OAGH | (12h 27m 21.65s , -18d 22m 03.8s) | C | 60 | 19.3 | 3823 | 2026-04-21 05:16:34 | MASTER-OAFA | (12h 40m 15.39s , -17d 23m 44.0s) | C | 60 | 20.1 | 3889 | 2026-04-21 05:17:40 | MASTER-OAFA | (12h 40m 15.43s , -17d 23m 43.4s) | C | 60 | 20.1 | 3930 | 2026-04-21 05:18:21 | MASTER-OAGH | (12h 34m 17.86s , -15d 53m 14.7s) | C | 60 | 19.4 | 3930 | 2026-04-21 05:18:21 | MASTER-OAGH | (12h 35m 37.05s , -16d 27m 06.0s) | C | 60 | 19.5 | 3955 | 2026-04-21 05:18:45 | MASTER-OAFA | (12h 40m 15.45s , -17d 23m 42.8s) | C | 60 | 20.2 | 4002 | 2026-04-21 05:19:32 | MASTER-OAGH | (12h 42m 42.14s , -15d 54m 17.4s) | C | 60 | 18.6 | 4002 | 2026-04-21 05:19:32 | MASTER-OAGH | (12h 44m 01.28s , -16d 28m 08.9s) | C | 60 | 18.9 | 4021 | 2026-04-21 05:19:51 | MASTER-OAFA | (12h 40m 15.46s , -17d 23m 42.1s) | C | 60 | 20.1 | 4087 | 2026-04-21 05:20:58 | MASTER-OAFA | (12h 40m 15.48s , -17d 23m 41.6s) | C | 60 | 20.1 | 4141 | 2026-04-21 05:21:51 | MASTER-OAGH | (12h 34m 22.53s , -19d 41m 12.5s) | C | 60 | 16.1 | 4141 | 2026-04-21 05:21:51 | MASTER-OAGH | (12h 35m 43.04s , -20d 15m 04.4s) | C | 60 | 15.7 | 4153 | 2026-04-21 05:22:04 | MASTER-OAFA | (12h 40m 15.50s , -17d 23m 41.3s) | C | 60 | 20.0 | 4212 | 2026-04-21 05:23:03 | MASTER-OAGH | (12h 42m 58.08s , -19d 42m 15.1s) | C | 60 | 18.5 | 4212 | 2026-04-21 05:23:03 | MASTER-OAGH | (12h 44m 18.55s , -20d 16m 07.7s) | C | 60 | 18.1 | 4219 | 2026-04-21 05:23:09 | MASTER-OAFA | (12h 40m 15.52s , -17d 23m 40.6s) | C | 60 | 20.1 | 4285 | 2026-04-21 05:24:15 | MASTER-OAFA | (12h 40m 15.55s , -17d 23m 40.1s) | C | 60 | 20.0 | 4341 | 2026-04-21 05:25:12 | MASTER-OAGH | (12h 34m 18.76s , -17d 47m 13.7s) | C | 60 | 18.2 | 4341 | 2026-04-21 05:25:12 | MASTER-OAGH | (12h 35m 38.65s , -18d 21m 04.7s) | C | 60 | 17.9 | 4350 | 2026-04-21 05:25:20 | MASTER-OAFA | (12h 40m 15.59s , -17d 23m 39.6s) | C | 60 | 20.0 | 4412 | 2026-04-21 05:26:23 | MASTER-OAGH | (12h 26m 01.58s , -17d 48m 10.3s) | C | 60 | 15.8 | 4412 | 2026-04-21 05:26:23 | MASTER-OAGH | (12h 27m 21.61s , -18d 22m 00.1s) | C | 60 | 16.0 | 4416 | 2026-04-21 05:26:26 | MASTER-OAFA | (12h 40m 15.62s , -17d 23m 39.2s) | C | 60 | 20.1 | 4482 | 2026-04-21 05:27:33 | MASTER-OAFA | (12h 40m 15.64s , -17d 23m 38.8s) | C | 60 | 19.9 | 4542 | 2026-04-21 05:28:33 | MASTER-OAGH | (12h 34m 16.69s , -15d 53m 12.9s) | C | 60 | 14.3 | 4547 | 2026-04-21 05:28:38 | MASTER-OAFA | (12h 40m 15.67s , -17d 23m 38.2s) | C | 60 | 20.0 | 4613 | 2026-04-21 05:29:44 | MASTER-OAGH | (12h 42m 41.80s , -15d 54m 16.3s) | C | 60 | 15.3 | 4613 | 2026-04-21 05:29:44 | MASTER-OAGH | (12h 44m 01.27s , -16d 28m 06.0s) | C | 60 | 14.9 | 4613 | 2026-04-21 05:29:44 | MASTER-OAFA | (12h 40m 15.70s , -17d 23m 37.8s) | C | 60 | 19.9 | 4679 | 2026-04-21 05:30:50 | MASTER-OAFA | (12h 40m 15.74s , -17d 23m 37.2s) | C | 60 | 20.0 | 4743 | 2026-04-21 05:31:54 | MASTER-OAGH | (12h 34m 21.40s , -19d 41m 10.3s) | C | 60 | 14.6 | 4743 | 2026-04-21 05:31:54 | MASTER-OAGH | (12h 35m 42.22s , -20d 15m 00.7s) | C | 60 | 14.5 | 4745 | 2026-04-21 05:31:55 | MASTER-OAFA | (12h 40m 15.77s , -17d 23m 37.0s) | C | 60 | 20.0 | 4810 | 2026-04-21 05:33:01 | MASTER-OAFA | (12h 40m 15.79s , -17d 23m 36.5s) | C | 60 | 20.1 | 4815 | 2026-04-21 05:33:05 | MASTER-OAGH | (12h 42m 56.35s , -19d 42m 13.4s) | C | 60 | 15.5 | 4815 | 2026-04-21 05:33:05 | MASTER-OAGH | (12h 44m 17.15s , -20d 16m 04.5s) | C | 60 | 15.2 | 4876 | 2026-04-21 05:34:07 | MASTER-OAFA | (12h 40m 15.81s , -17d 23m 36.3s) | C | 60 | 20.0 | 4941 | 2026-04-21 05:35:12 | MASTER-OAFA | (12h 40m 15.84s , -17d 23m 36.4s) | C | 60 | 20.0 | 4954 | 2026-04-21 05:35:24 | MASTER-OAGH | (12h 34m 19.16s , -17d 47m 10.7s) | C | 60 | 14.1 | 5007 | 2026-04-21 05:36:17 | MASTER-OAFA | (12h 40m 15.86s , -17d 23m 35.7s) | C | 60 | 20.0 | 5073 | 2026-04-21 05:37:24 | MASTER-OAFA | (12h 40m 15.87s , -17d 23m 35.3s) | C | 60 | 19.9 | 5138 | 2026-04-21 05:38:29 | MASTER-OAFA | (12h 40m 15.91s , -17d 23m 35.2s) | C | 60 | 19.9 | 5184 | 2026-04-21 05:39:15 | MASTER-OAGH | (12h 34m 16.09s , -15d 53m 00.5s) | C | 60 | 17.1 | 5184 | 2026-04-21 05:39:15 | MASTER-OAGH | (12h 35m 37.14s , -16d 26m 52.1s) | C | 60 | 17.1 | 5204 | 2026-04-21 05:39:35 | MASTER-OAFA | (12h 40m 15.93s , -17d 23m 34.8s) | C | 60 | 19.9 | 5256 | 2026-04-21 05:40:27 | MASTER-OAGH | (12h 42m 39.48s , -15d 54m 07.1s) | C | 60 | 17.1 | 5256 | 2026-04-21 05:40:27 | MASTER-OAGH | (12h 44m 00.43s , -16d 27m 59.1s) | C | 60 | 16.8 | 5270 | 2026-04-21 05:40:41 | MASTER-OAFA | (12h 40m 15.94s , -17d 23m 34.3s) | 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/44367. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42488] GRB 260421B: BOOTES-7 early optical afterglow detection
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44366 SUBJECT: GRB 260421B: BOOTES-7 early optical afterglow detection DATE: 26/04/21 05:37:53 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct(a)iaa.es> S.-Y. Wu, M. Gritsevich, I. Perez-Garcia, E. Fernandez-Garcia, M. D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy, and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar (Univ. of Malaga), Y.-D. Hu (GXU, Guanxi), B.-B. Zhang (Nanjing Univ.), and A. Maury (Space Obs., San Pedro de Atacama), on behalf of a larger collaboration, report: Following the detection of GRB 260421B by Fermi (Fermi Team, GCN 44360, Preis and Greiner, GCN 44361) and SVOM (Zhao et al. GCN 44362), the BOOTES-7 telescope at the 0.6m BOOTES-7 robotic telescope at Space Observatory (San Pedro de Atacama, Chile) automatically observed the GRB location starting on Aug. 21, 04:28:36 UT (i.e. 15 min after GRB onset). A series of images in clear filter were gathered and we identify the fading optical afterglow reported by He et al. (GCN 44363) Sánchez-Álvarez et al. (GCN 44364) and Turpin et al. (GCN 44365) at coordinates RA: 12:40:00.50 Dec: -17:44:24.0 (+/- 0.5 “). Preliminary magnitude is 18. Further data analysis is ongoing. We would like to thank the staff at San Pedro de Atacama Space Observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/44366. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42487] GRB 260421B: LCO optical afterglow confirmation
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44365 SUBJECT: GRB 260421B: LCO optical afterglow confirmation DATE: 26/04/21 05:32:17 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> D. Turpin (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), A. Saccardi (CEA/Irfu), C. Wu (NAOC), J. T. Palmerio (CEA/Irfu), L. P. Xin (NAOC), B. Cordier (CEA/Irfu), W.-L Zhang (PMO), Z.-Y Liu (GZNU), report on behalf of the SVOM mission team: We observed the field of GRB 260421B detected by SVOM (Zhao et al., GCN 44362) and Fermi/GBM (The Fermi GBM team, GCN 44360) with the LCO 1m telescope at Cerro Tololo Observatory equipped with the Sinistro instrument. Our observation started at 2026-04-21T04:29:54.940 about 16.5 min after the SVOM/ECLAIRs trigger time. We obtained 3x200 s exposures in the SDSS r and PanSTARRS-z filters. An uncatalogued bright optical candidate is well detected in our single images at RA, dec (J2000) = 190.00203, -17.74017 (err = 0.5 arcsec). This position is consistent with the optical counterpart reported by the TRT telescope (He et al, GCN 44363) and the SVOM/COLIBRI FM-GFT (Álvarez et al. GCN 43646). We measure the following magnitude calibrated against the PanSTARRS DR1 catalog, and not corrected for Galactic extinction: r = 18.47 +/- 0.01 (AB) (Tmid - T0 = 18.2 min) z = 18.92 +/- 0.09 (AB) (Tmid - T0 = 30.7 min) This project is funded by the SVOM collaboration. Further observations are scheduled. View this GCN Circular online at https://gcn.nasa.gov/circulars/44365. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42486] GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44364 SUBJECT: GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart DATE: 26/04/21 05:28:06 GMT FROM: freddalvarez(a)astro.unam.mx Fredd Sánchez Álvarez (UNAM), Nikos Mandarakas (LAM), Alan M. Watson (UNAM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (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), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), W.L. Zhang (PMO), and Z. Y. Liu (GZNU) report: We imaged the field of the SVOM/ECLAIRs and Fermin/GBM GRB 260421B (Zhao et al., GCN Circ. 44362; Fermi GBM Team, GCN Circ. 44360) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-21 04:15:13 to 04:30:07 (from 1.9 to 16.8 minutes after the trigger) and obtained 430 seconds of simultaneous exposure in the r/z filters. The data were reduced, coadded, calibrated, 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 detect an uncatalogued source consistent with the ECLAIRs localization at: RA(J2000) = 12:40:00.48 = 190.00200 degrees Dec(J2000) = -17:44:24.6 = -17.74015 degrees with an uncertainty of 0.5 arcsec. The source was detected in both r and z and was observed to fade from r ≈ 14.5 to r ≈ 18.3 during our observations. The color of the source was r - z ≈ 0.45 +/- 0.02, which is consistent with the expectations for an afterglow. We suggest this is the optical counterpart of the GRB. Subsequent imaging in the g/r/i/z/y filters show detections in all bands, indicating that the redshift is less than 3.5. We encourage spectroscopic observations of the source. Further observations are planned. 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/44364. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42485] GRB 260421B: TRT optical counterpart detection
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44363 SUBJECT: GRB 260421B: TRT optical counterpart detection DATE: 26/04/21 05:26:32 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L.B. He (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), X. Liu, Z.P. Zhu, S.Q. Jiang, J. An, D. Xu (NAOC) report: We observed the field of GRB 260421B detected by Fermi (GCN 44360) and SVOM (zhao et al., GCN 44362), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile (CTO). We obtained a series of frames in the r-band. An uncatalogued source is detected within the Fermi error circle at coordinates R.A. (J2000) = 12:40:00.5 Dec. (J2000) = -17:44:24.5 with an uncertainty of ~ 1.0 arcsec. The source had r = 19.14 +/- 0.07 mag, calibrated with Pan-STARRS DR2 and not corrected for Galactic extinction. No NEO would be at the above position at the observational time by checking MPC. We thus think the source is the optical counterpart of GRB 260421B. View this GCN Circular online at https://gcn.nasa.gov/circulars/44363. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42484] GRB 260421B: SVOM detection of a long burst
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44362 SUBJECT: GRB 260421B: SVOM detection of a long burst DATE: 26/04/21 05:20:23 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> D.Zhao (NAOC), H.Goto (RIKEN), W. L. Zhang (PMO), Z. Y. Liu (GZNU) report on behalf of the SVOM mission team: At 2026-04-21T04:13:25 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260421B (SVOM burst-id sb26042105). The Fermi GBM also detected this burst (GCN 44360 & 44361). 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 13 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 30.71 in the [8-120] keV energy band over a time window of 20.48 seconds starting at 2026-04-21T04:13:17. The localization of the best alert is R.A., Dec. 189.9811, -17.7676 degrees (J2000) with a 90% confidence level (C.L.) radius of 3.21 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve showed a multiple peak structure with a T90 duration of about 52.824 (-0.172 +0.169). This burst also triggered SVOM/GRM at 2026-04-21T04:13:21 on a timescale of 1 seconds with an SNR of 7.90. The SVOM/GRM light curve showed a multiple peak structure with a T90 duration of about 20.04 (-0.93 +3.07). SVOM slewed to the burst. SVOM/MXT began observing the field at 2026-04-21T04:18:40 UTC, 315 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 190.0318, -17.7566 degrees: R.A. (J2000) = 12h40m07.62s Dec. (J2000) = -17d45m23.69s with a 90% C.L. radius of 97.27 arcseconds. This location is 2.97 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. VT began observing the field after the slew. The analysis of the data will be published in a future circular. 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 W. L. Zhang: wlzhang(a)pmo.ac.cn Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44362. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42483] GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44361 SUBJECT: GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176) DATE: 26/04/21 04:54:24 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 798437606 at 04:13:21 on 21 April 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) = 190.5 deg Decl.(2000.0) = -16.5 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/GRB260421176/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB260421176/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB260421176/json View this GCN Circular online at https://gcn.nasa.gov/circulars/44361. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42482] GRB 260421B: Fermi GBM Final Real-time Localization
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44360 SUBJECT: GRB 260421B: Fermi GBM Final Real-time Localization DATE: 26/04/21 04:22:36 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 04:13:21 UT on 21 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260421B (trigger 798437606.166588 / 260421176). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 188.8, Dec = -17.8 (J2000 degrees, equivalent to J2000 12h 35m, -17d 48'), with a statistical uncertainty of 2.4 degrees. The angle from the Fermi LAT boresight is 58.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260421176/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260421176/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260421176/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44360. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42481] Fermi GRB 260421A: Global MASTER-Net observations report
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44359 SUBJECT: Fermi GRB 260421A: Global MASTER-Net observations report DATE: 26/04/21 03:16:41 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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260421A ( Fermi GBM team, GCN 44358) errorbox 3101 sec after notice time and 3131 sec after trigger time at 2026-04-21 03:04:55 UT, with upper limit up to 19.4 mag. Observations started at twilight. The observations began at zenith distance = 47 deg. The sun altitude is -16.0 deg. The galactic latitude b = 54 deg., longitude l = 118 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3262778 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 3162 | 2026-04-21 03:04:55 | MASTER-OAGH | (13h 20m 14.14s , +62d 00m 28.6s) | C | 60 | 18.8 | 3162 | 2026-04-21 03:04:55 | MASTER-OAGH | (13h 22m 34.25s , +61d 26m 33.6s) | C | 60 | 19.2 | 3234 | 2026-04-21 03:06:08 | MASTER-OAGH | (13h 37m 23.83s , +62d 00m 57.1s) | C | 60 | 18.8 | 3234 | 2026-04-21 03:06:08 | MASTER-OAGH | (13h 39m 43.36s , +61d 26m 60.0s) | C | 60 | 19.2 | 3426 | 2026-04-21 03:09:20 | MASTER-OAGH | (13h 07m 30.22s , +63d 21m 09.2s) | C | 60 | 19.4 | 3426 | 2026-04-21 03:09:20 | MASTER-OAGH | (13h 04m 59.80s , +63d 55m 03.4s) | C | 60 | 19.0 | 3497 | 2026-04-21 03:10:31 | MASTER-OAGH | (13h 25m 34.30s , +63d 20m 22.6s) | C | 60 | 19.4 | 3497 | 2026-04-21 03:10:31 | MASTER-OAGH | (13h 23m 04.46s , +63d 54m 18.8s) | C | 60 | 19.0 | 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/44359. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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