TITLE: GCN CIRCULAR NUMBER: 39052 SUBJECT: Fermi GRB 250128A: Global MASTER-Net observations report DATE: 25/01/28 11:32:15 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs lipunov@xray.sai.msu.ru

V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, 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. 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 (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB 250128A ( Fermi GBM team, GCN 39051) errorbox 568 sec after notice time and 595 sec after trigger time at 2025-01-28 10:43:38 UT, with upper limit up to 15.8 mag. Observations started at twilight. The observations began at zenith distance = 53 deg. The sun altitude is -8.6 deg.

The galactic latitude b = 23 deg., longitude l = 93 deg.

Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2758800

We obtain a following upper limits.

Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________

597 | 2025-01-28 10:43:38 | MASTER-Tunka | (18h 55m 15.13s , +62d 26m 57.5s) | C | 1 | 15.2 | 598 | 2025-01-28 10:43:38 | MASTER-Tunka | (18h 55m 15.13s , +62d 26m 57.5s) | C | 3 | 15.8 | Coadd 602 | 2025-01-28 10:43:43 | MASTER-Tunka | (18h 55m 15.05s , +62d 26m 57.5s) | C | 1 | 15.1 | 608 | 2025-01-28 10:43:49 | MASTER-Tunka | (18h 55m 15.04s , +62d 26m 56.9s) | C | 1 | 15.1 | 613 | 2025-01-28 10:43:54 | MASTER-Tunka | (18h 55m 15.13s , +62d 26m 56.7s) | C | 1 | 15.3 | Filter C is a clear (unfiltred) band.

The observation and reduction will continue. The message may be cited.

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