TITLE: GCN CIRCULAR NUMBER: 39599 SUBJECT: Fermi GRB 250305A: Global MASTER-Net observations report DATE: 25/03/05 21:32:49 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 250305A ( Fermi GBM team, GCN 39597) errorbox 20388 sec after notice time and 20424 sec after trigger time at 2025-03-05 21:09:22 UT, with upper limit up to 18.6 mag. The observations began at zenith distance = 78 deg. The sun altitude is -45.2 deg.

The galactic latitude b = 47 deg., longitude l = 353 deg.

Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2801332

We obtain a following upper limits.

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

20455 | 2025-03-05 21:09:22 | MASTER-SAAO | (14h 34m 50.28s , -02d 29m 23.3s) | C | 60 | 18.3 | 20534 | 2025-03-05 21:10:41 | MASTER-SAAO | (14h 42m 45.22s , -02d 30m 38.4s) | C | 60 | 18.4 | 20613 | 2025-03-05 21:12:01 | MASTER-SAAO | (14h 36m 36.01s , -04d 22m 25.4s) | C | 60 | 18.6 | 20772 | 2025-03-05 21:14:39 | MASTER-SAAO | (14h 44m 39.80s , -04d 22m 36.6s) | C | 60 | 18.5 | Filter C is a clear (unfiltred) band.

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

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