TITLE: GCN CIRCULAR NUMBER: 42439 SUBJECT: GRB 251025B: MASTER OT detection DATE: 25/10/25 16:28:10 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru> O.Gress, N.Budnev (Irkutsk State University), V. Lipunov, P.Balanutsa, I.Panchenko, A.Kuznetsov, G.Antipov, E.Gorbovskoy, K.Zhirkov, N.Tiurina, A.Sankovich, Ya.Kechin, A.Chasovnikov, V.Topolev, D.Vlasenko, V.Senik, D.Vlasenko, V.Shumkov, K.Vetrov, Yu. Tselik(Lomonosov MSU, SAI, Moscow), R.Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA, San Juan Uni.,Argentina); D.Buckley (SAAO, South Africa), O.Ershova (ISU, Irkutsk), A.Sosnovskij (CrAO RAS), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias, Spain), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella,L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico) MASTER Global Robotic Net [1-4] started Svom GRB 251025B (Hussein et al. GCN 42437, Ttrigger= 2025-10-25 14:24:05UT) at MASTER-Tunka and at MASTER-Kislovodsk. There is MASTER OT J015807.49+301814.0 with unfiltered m_OT=19.0 at at 2025-10-25 14:36:20 (mlim=20.5) Observation and reduction will be continued. This OT was discovered by SVOM (Chao Wu et al. GCN 42438, first image at 2025-10-25T14:25:38) [1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L [2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271 [3] Lipunov et a. 2019, ARep, vol.63, 293 [4] Lipunov V., Kornilov V., Gorbovskoy E., Tiurina N., Kuznetsov A. 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics,Lomonosov MSU PRESS, 591pp. http://www.pereplet.ru/lipunov/625.html#625 View this GCN Circular online at https://gcn.nasa.gov/circulars/42439. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...