TITLE: GCN CIRCULAR NUMBER: 44370 SUBJECT: Fermi GRB 260421C: Global MASTER-Net observations report DATE: 26/04/21 09:30:49 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@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 260421C ( Fermi GBM team, GCN 44369) errorbox 165 sec after notice time and 186 sec after trigger time at 2026-04-21 08:28:26 UT, with upper limit up to 20.5 mag. The observations began at zenith distance = 51 deg. The sun altitude is -43.9 deg. The galactic latitude b = 19 deg., longitude l = 96 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3263342 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 217 | 2026-04-21 08:28:26 | MASTER-OAGH | (19h 25m 37.26s , +63d 45m 12.4s) | C | 60 | 19.6 | 217 | 2026-04-21 08:28:26 | MASTER-OAGH | (19h 28m 03.53s , +63d 11m 30.5s) | C | 60 | 19.8 | 290 | 2026-04-21 08:29:39 | MASTER-OAGH | (19h 43m 37.39s , +63d 44m 07.3s) | C | 60 | 19.6 | 290 | 2026-04-21 08:29:39 | MASTER-OAGH | (19h 46m 02.78s , +63d 10m 22.7s) | C | 60 | 19.9 | 518 | 2026-04-21 08:33:28 | MASTER-OAGH | (19h 26m 38.22s , +59d 56m 08.4s) | C | 60 | 20.0 | 518 | 2026-04-21 08:33:28 | MASTER-OAGH | (19h 28m 49.30s , +59d 22m 23.7s) | C | 60 | 20.2 | 736 | 2026-04-21 08:36:35 | MASTER-OAGH | (19h 39m 52.48s , +63d 57m 57.9s) | C | 120 | 19.9 | 856 | 2026-04-21 08:36:35 | MASTER-OAGH | (19h 39m 52.48s , +63d 57m 57.9s) | C | 360 | 20.5 | Coadd 736 | 2026-04-21 08:36:35 | MASTER-OAGH | (19h 42m 20.57s , +63d 24m 11.2s) | C | 120 | 20.1 | 856 | 2026-04-21 08:36:35 | MASTER-OAGH | (19h 42m 20.57s , +63d 24m 11.2s) | C | 360 | 20.5 | Coadd 936 | 2026-04-21 08:39:55 | MASTER-OAGH | (19h 39m 52.89s , +63d 57m 53.5s) | C | 120 | 19.9 | 936 | 2026-04-21 08:39:55 | MASTER-OAGH | (19h 42m 21.02s , +63d 24m 06.6s) | C | 120 | 20.1 | 1066 | 2026-04-21 08:42:05 | MASTER-OAGH | (19h 39m 58.99s , +63d 56m 50.1s) | C | 120 | 20.0 | 1066 | 2026-04-21 08:42:05 | MASTER-OAGH | (19h 42m 27.17s , +63d 23m 03.5s) | C | 120 | 20.2 | 1197 | 2026-04-21 08:44:16 | MASTER-OAGH | (19h 39m 53.32s , +63d 57m 47.2s) | C | 120 | 20.0 | 1197 | 2026-04-21 08:44:16 | MASTER-OAGH | (19h 42m 21.81s , +63d 24m 00.3s) | C | 120 | 20.2 | 1328 | 2026-04-21 08:46:27 | MASTER-OAGH | (19h 39m 59.23s , +63d 56m 43.3s) | C | 120 | 19.9 | 1328 | 2026-04-21 08:46:27 | MASTER-OAGH | (19h 42m 27.64s , +63d 22m 56.8s) | C | 120 | 20.2 | 2193 | 2026-04-21 09:01:22 | MASTER-OAGH | (19h 26m 48.80s , +59d 56m 20.2s) | C | 60 | 19.9 | 2193 | 2026-04-21 09:01:22 | MASTER-OAGH | (19h 29m 01.44s , +59d 22m 30.8s) | C | 60 | 20.0 | 2326 | 2026-04-21 09:03:35 | MASTER-OAGH | (19h 17m 11.76s , +61d 50m 25.1s) | C | 60 | 19.7 | 2326 | 2026-04-21 09:03:35 | MASTER-OAGH | (19h 19m 32.38s , +61d 16m 36.3s) | C | 60 | 19.9 | 2397 | 2026-04-21 09:04:46 | MASTER-OAGH | (19h 34m 03.19s , +61d 49m 16.1s) | C | 60 | 19.5 | 2397 | 2026-04-21 09:04:46 | MASTER-OAGH | (19h 36m 23.31s , +61d 15m 26.3s) | C | 60 | 19.9 | 2557 | 2026-04-21 09:06:57 | MASTER-OAGH | (19h 51m 54.15s , +63d 51m 04.9s) | C | 120 | 19.9 | 2557 | 2026-04-21 09:06:57 | MASTER-OAGH | (19h 54m 23.17s , +63d 17m 13.8s) | C | 120 | 20.0 | 2688 | 2026-04-21 09:09:07 | MASTER-OAGH | (19h 52m 00.00s , +63d 50m 02.0s) | C | 120 | 19.9 | 2688 | 2026-04-21 09:09:07 | MASTER-OAGH | (19h 54m 29.04s , +63d 16m 12.0s) | C | 120 | 19.9 | 2819 | 2026-04-21 09:11:18 | MASTER-OAGH | (19h 50m 19.75s , +64d 50m 59.2s) | C | 120 | 19.6 | 2819 | 2026-04-21 09:11:18 | MASTER-OAGH | (19h 52m 54.24s , +64d 17m 09.7s) | C | 120 | 19.6 | 2950 | 2026-04-21 09:13:29 | MASTER-OAGH | (19h 50m 26.43s , +64d 49m 56.1s) | C | 120 | 19.8 | 2950 | 2026-04-21 09:13:29 | MASTER-OAGH | (19h 53m 00.91s , +64d 16m 07.5s) | C | 120 | 19.8 | 3125 | 2026-04-21 09:16:54 | MASTER-OAGH | (19h 26m 53.60s , +59d 55m 26.9s) | C | 60 | 19.4 | 3125 | 2026-04-21 09:16:54 | MASTER-OAGH | (19h 29m 07.76s , +59d 21m 41.7s) | C | 60 | 19.4 | 3197 | 2026-04-21 09:18:06 | MASTER-OAGH | (19h 17m 13.13s , +61d 50m 46.4s) | C | 60 | 19.4 | 3197 | 2026-04-21 09:18:06 | MASTER-OAGH | (19h 19m 35.44s , +61d 17m 01.7s) | C | 60 | 19.5 | 3305 | 2026-04-21 09:19:24 | MASTER-OAGH | (19h 36m 06.37s , +65d 49m 10.5s) | C | 120 | 19.7 | 3305 | 2026-04-21 09:19:24 | MASTER-OAGH | (19h 38m 48.49s , +65d 15m 24.8s) | C | 120 | 19.8 | 3436 | 2026-04-21 09:21:35 | MASTER-OAGH | (19h 36m 10.81s , +65d 50m 43.9s) | C | 120 | 19.3 | 3436 | 2026-04-21 09:21:35 | MASTER-OAGH | (19h 38m 53.00s , +65d 16m 58.7s) | C | 120 | 19.5 | 3567 | 2026-04-21 09:23:46 | MASTER-OAGH | (19h 24m 08.88s , +65d 49m 56.4s) | C | 120 | 19.5 | 3567 | 2026-04-21 09:23:46 | MASTER-OAGH | (19h 26m 51.43s , +65d 16m 11.7s) | C | 120 | 19.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44370. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...