TITLE: GCN CIRCULAR NUMBER: 39689 SUBJECT: Swift GRB 250312A: Global MASTER-Net observations report DATE: 25/03/12 18:04:11 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs 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) was pointed to the Swift GRB 250312A ( A. Melandri et al., GCN 39686) errorbox 15966 sec after notice time and 16003 sec after trigger time at 2025-03-12 17:51:00 UT, with upper limit up to 18.2 mag. Observations started at twilight. The observations began at zenith distance = 54 deg. The sun altitude is -11.5 deg. The galactic latitude b = -69 deg., longitude l = 264 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2809737 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 16093 | MASTER-SAAO | C | 180 | 17.1 | 16292 | MASTER-SAAO | C | 180 | 18.2 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.