TITLE: GCN CIRCULAR NUMBER: 39620 SUBJECT: Fermi GRB 250307A: Global MASTER-Net observations report DATE: 25/03/08 00:30:39 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-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 250307A ( Fermi GBM team, GCN 39618) errorbox 12559 sec after notice time and 12601 sec after trigger time at 2025-03-07 23:27:54 UT, with upper limit up to 17.9 mag. The observations began at zenith distance = 70 deg. The sun altitude is -42.9 deg.

The galactic latitude b = 16 deg., longitude l = 27 deg.

Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2803750

We obtain a following upper limits.

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

12631 | 2025-03-07 23:27:54 | MASTER-Kislovodsk | (17h 39m 34.52s , +03d 16m 16.2s) | C | 60 | 16.0 | 13390 | 2025-03-07 23:40:34 | MASTER-Kislovodsk | (17h 47m 30.44s , +03d 15m 20.9s) | C | 60 | 16.9 | 13470 | 2025-03-07 23:41:53 | MASTER-Kislovodsk | (17h 39m 36.28s , +03d 16m 01.7s) | C | 60 | 17.1 | 13550 | 2025-03-07 23:43:13 | MASTER-Kislovodsk | (17h 38m 11.65s , +01d 21m 58.9s) | C | 60 | 16.9 | 15377 | 2025-03-08 00:13:10 | MASTER-Kislovodsk | (17h 40m 28.55s , +02d 25m 26.0s) | C | 120 | 17.0 | 15517 | 2025-03-08 00:15:30 | MASTER-Kislovodsk | (17h 40m 32.95s , +02d 24m 17.6s) | C | 120 | 17.7 | 15656 | 2025-03-08 00:17:49 | MASTER-Kislovodsk | (17h 40m 27.31s , +00d 23m 17.3s) | C | 120 | 17.9 | 15796 | 2025-03-08 00:20:09 | MASTER-Kislovodsk | (17h 40m 31.50s , +00d 23m 28.7s) | C | 120 | 17.9 | 16015 | 2025-03-08 00:24:18 | MASTER-Kislovodsk | (17h 40m 31.73s , +02d 23m 54.6s) | C | 60 | 17.1 | 16095 | 2025-03-08 00:25:39 | MASTER-Kislovodsk | (17h 46m 12.95s , +01d 24m 43.6s) | C | 60 | 17.4 | Filter C is a clear (unfiltred) band.

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

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