TITLE: GCN CIRCULAR NUMBER: 40179 SUBJECT: GRB 250419A: MASTER optical afterglow observation DATE: 25/04/19 17:43:59 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru> V.Lipunov, A.Kuznetsov, G.Antipov, V.Topolev, K.Zhirkov, N.Tyurina, P.Balanutsa, A.Chasovnikov, Ya.Kechin, V.Senik, K. Labzina, D.Vlasenko, E.Gorboskoy(Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (OAFA), A.Sosnovskij (Crao RAS), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), R.Rebolo (The Instituto de Astrofisica de Canarias), D.Buckley (SAAO), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro AstrophysicsObservatory) MASTER-OAFA robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru,Lipunov et al., 2010, Advances in Astronomy, v. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the SVOM Alert 250419.10 (trigger No 1745029772,13h 29m 32.88s , +07d 05m 09.6s, R=0.1525, Wang et al. GCN 40168, Ocelotl López et al. GCN40169, Xin etl al. GCN40170) 3960 sec after trigger time at 2025-04-19 03:35:32 UT, with upper limit up to 19.9 mag. The observations began at zenith distance = 39 deg. The sun altitude is -66.0 deg. The galactic latitude b = 68 deg., longitude l = 330 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2847195 We obtained the following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment 3991 | 2025-04-19 03:35:32 | MASTER-OAFA | (13h 29m 02.64s , +07d 04m 50.6s) | C | 60 | 19.7 | 5446 | 2025-04-19 03:59:47 | MASTER-OAFA | (13h 28m 54.60s , +07d 03m 09.9s) | C | 60 | 19.7 | 6895 | 2025-04-19 04:23:56 | MASTER-OAFA | (13h 29m 35.13s , +07d 25m 23.4s) | C | 60 | 19.6 | 6955 | 2025-04-19 04:23:56 | MASTER-OAFA | (13h 29m 35.12s , +07d 25m 23.4s) | C | 180 | 19.9 | Coadd 8383 | 2025-04-19 04:48:45 | MASTER-OAFA | (13h 29m 28.53s , +07d 25m 00.4s) | C | 60 | 19.5 | 9666 | 2025-04-19 05:10:08 | MASTER-OAFA | (13h 29m 34.89s , +07d 26m 24.5s) | C | 60 | 19.4 | 10159 | 2025-04-19 05:18:20 | MASTER-OAFA | (13h 29m 31.07s , +07d 26m 26.7s) | C | 60 | 19.5 | Filter C is a clear (unfiltred) band. There is MASTER OT J132937.28+070227.8 since 2025-04-19 03:35:32 with m_OT=18.0 (unfiltered, Lipunov et al. 2010, 2019, 2022, 2023) up to 2025-04-19 05:18:20UT at SVOM VT position (GCN 40170 Xin et al.) The reduction will be continued View this GCN Circular online at https://gcn.nasa.gov/circulars/40179. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...