TITLE: GCN CIRCULAR NUMBER: 44826 SUBJECT: Fermi GRB 260604C: Global MASTER-Net observations report DATE: 26/06/04 21:20:24 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), M. Segura, 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-Tavrida robotic telescope [1] located in Russia (Lomonosov MSU, SAI Crimea astronomical station) started inspect of the Fermi GRB 260604C ( Fermi GBM team, GCN 44822) errorbox 68 sec after notice time and 121 sec after trigger time at 2026-06-04 20:20:45 UT, with upper limit up to 19.9 mag. The observations began at zenith distance = 13 deg. The sun altitude is -20.4 deg. MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260604C errorbox 2607 sec after notice time and 2660 sec after trigger time at 2026-06-04 21:03:04 UT, with upper limit up to 18.5 mag. The observations began at zenith distance = 28 deg. The sun altitude is -23.8 deg. The galactic latitude b = 65 deg., longitude l = 54 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3361051 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 132 | 2026-06-04 20:20:45 | MASTER-Tavrida | (14h 45m 39.13s , +34d 23m 10.1s) | C | 20 | 18.2 | 159 | 2026-06-04 20:21:08 | MASTER-Tavrida | (14h 45m 39.22s , +34d 23m 08.2s) | C | 30 | 18.5 | 201 | 2026-06-04 20:21:45 | MASTER-Tavrida | (14h 45m 39.31s , +34d 23m 05.7s) | C | 40 | 18.7 | 244 | 2026-06-04 20:22:28 | MASTER-Tavrida | (14h 45m 39.40s , +34d 23m 03.5s) | C | 40 | 18.7 | 292 | 2026-06-04 20:23:11 | MASTER-Tavrida | (14h 45m 39.48s , +34d 23m 00.9s) | C | 50 | 18.9 | 351 | 2026-06-04 20:24:05 | MASTER-Tavrida | (14h 45m 39.57s , +34d 22m 58.3s) | C | 60 | 19.0 | 424 | 2026-06-04 20:25:08 | MASTER-Tavrida | (14h 45m 39.70s , +34d 22m 55.4s) | C | 80 | 19.9 | 512 | 2026-06-04 20:26:31 | MASTER-Tavrida | (14h 45m 39.83s , +34d 22m 52.2s) | C | 90 | 18.1 | 616 | 2026-06-04 20:28:05 | MASTER-Tavrida | (14h 45m 39.93s , +34d 22m 49.5s) | C | 110 | 18.8 | 753 | 2026-06-04 20:30:17 | MASTER-Tavrida | (14h 41m 46.90s , +33d 53m 19.6s) | C | 120 | 19.3 | 2690 | 2026-06-04 21:03:04 | MASTER-Kislovodsk | (14h 31m 34.56s , +34d 00m 31.5s) | C | 60 | 18.4 | 2780 | 2026-06-04 21:04:34 | MASTER-Kislovodsk | (14h 41m 05.21s , +33d 59m 44.5s) | C | 60 | 18.5 | 2868 | 2026-06-04 21:06:02 | MASTER-Kislovodsk | (14h 36m 52.22s , +35d 55m 19.9s) | C | 60 | 18.3 | 2957 | 2026-06-04 21:07:31 | MASTER-Kislovodsk | (14h 46m 41.72s , +35d 54m 08.3s) | C | 60 | 18.4 | 3046 | 2026-06-04 21:09:00 | MASTER-Kislovodsk | (14h 45m 53.08s , +34d 00m 34.0s) | C | 60 | 18.5 | 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/44826. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...