TITLE: GCN CIRCULAR NUMBER: 40352 SUBJECT: Fermi GRB 250505A: Global MASTER-Net observations report DATE: 25/05/05 17:15:53 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), 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.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-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 250505A ( Fermi GBM team, GCN 40348) errorbox 31206 sec after notice time and 31236 sec after trigger time at 2025-05-05 16:49:16 UT, with upper limit up to 18.5 mag. Observations started at twilight. The observations began at zenith distance = 37 deg. The sun altitude is -11.5 deg.

The galactic latitude b = -3 deg., longitude l = 223 deg.

Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2861221

We obtain a following upper limits.

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

31267 | 2025-05-05 16:49:16 | MASTER-SAAO | (06h 52m 27.70s , -10d 20m 11.1s) | C | 60 | 18.0 | 31346 | 2025-05-05 16:50:35 | MASTER-SAAO | (07h 00m 40.59s , -10d 18m 52.3s) | C | 60 | 17.9 | 31426 | 2025-05-05 16:51:55 | MASTER-SAAO | (06h 55m 08.68s , -12d 12m 30.2s) | C | 60 | 18.1 | 31506 | 2025-05-05 16:53:15 | MASTER-SAAO | (07h 03m 25.46s , -12d 13m 27.5s) | C | 60 | 18.0 | 31586 | 2025-05-05 16:54:35 | MASTER-SAAO | (06h 50m 15.46s , -08d 25m 58.2s) | C | 60 | 18.2 | 32311 | 2025-05-05 17:06:40 | MASTER-SAAO | (06h 52m 25.86s , -10d 18m 53.6s) | C | 60 | 18.5 | 32390 | 2025-05-05 17:07:59 | MASTER-SAAO | (07h 00m 29.83s , -10d 19m 51.8s) | C | 60 | 18.3 | Filter C is a clear (unfiltred) band.

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

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