TITLE: GCN CIRCULAR NUMBER: 40092 SUBJECT: Fermi trigger No 765619921: Global MASTER-Net observations report DATE: 25/04/06 13:46:45 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB250406.34 (trigger No 765619921,16h 27m 07.92s , +59d 07m 01.2s, R=50) errorbox 915 sec after notice time and 949 sec after trigger time at 2025-04-06 08:27:46 UT, with upper limit up to 20.0 mag. The observations began at zenith distance = 49 deg. The sun altitude is -30.9 deg.

MASTER-Tunka robotic telescope located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB250406.34 errorbox 18661 sec after notice time and 18696 sec after trigger time at 2025-04-06 13:23:33 UT, with upper limit up to 18.3 mag. Observations started at twilight. The observations began at zenith distance = 73 deg. The sun altitude is -14.9 deg.

The galactic latitude b = 41 deg., longitude l = 89 deg.

Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2834649

We obtain a following upper limits.

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

970 | 2025-04-06 08:27:46 | MASTER-OAFA | (15h 28m 20.65s , +13d 16m 46.0s) | C | 40 | 18.2 | 980 | 2025-04-06 08:27:46 | MASTER-OAFA | (15h 19m 00.28s , +12d 54m 07.9s) | C | 60 | 20.0 | 2262 | 2025-04-06 08:49:18 | MASTER-OAFA | (15h 28m 22.19s , +13d 17m 10.6s) | C | 40 | 18.3 | 2272 | 2025-04-06 08:49:18 | MASTER-OAFA | (15h 19m 02.07s , +12d 54m 31.6s) | C | 60 | 20.0 | 3654 | 2025-04-06 09:12:30 | MASTER-OAFA | (15h 28m 15.85s , +13d 17m 06.0s) | C | 40 | 18.3 | 3665 | 2025-04-06 09:12:31 | MASTER-OAFA | (15h 18m 56.28s , +12d 54m 26.8s) | C | 60 | 20.0 | 5045 | 2025-04-06 09:35:41 | MASTER-OAFA | (15h 28m 20.02s , +13d 18m 20.6s) | C | 40 | 18.2 | 5055 | 2025-04-06 09:35:41 | MASTER-OAFA | (15h 19m 00.70s , +12d 55m 40.3s) | C | 60 | 20.0 | 18727 | 2025-04-06 13:23:33 | MASTER-Tunka | (18h 23m 55.12s , +49d 33m 54.6s) | C | 60 | 18.2 | 18995 | 2025-04-06 13:28:01 | MASTER-Tunka | (18h 23m 53.09s , +49d 33m 24.0s) | C | 60 | 18.0 | 19206 | 2025-04-06 13:31:32 | MASTER-Tunka | (18h 23m 50.27s , +49d 34m 17.4s) | C | 60 | 18.2 | 19597 | 2025-04-06 13:38:03 | MASTER-Tunka | (18h 23m 50.38s , +49d 32m 59.3s) | 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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