TITLE: GCN CIRCULAR NUMBER: 42838 SUBJECT: Fermi GRB 251125B : MASTER OT J155558.56+581224.1 optical counterpart discovery DATE: 25/11/25 23:04:15 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru> O.A.Gress, N.M.Budnev (Irkutsk State University), V.M. Lipunov, A.Kuznetsov, I.Panchenko, E.Gorbovskoy, G.Antipov, P.Balanutsa, V.Senik, I.Panchenko, N. Tiurina, K.Zhirkov, Ya.Kechin, A.Chasovnikov, V.Topolev, D.Vlasenko, 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 (Irkutsk State University), A. Sosnovskij (CrAO RAS), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico) V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias,Spain), MASTER-Tunka robotic telescope (Global MASTER-Net [1-4], http://observ.pereplet.ru) started inspect (Lipunov et al. GCN 42837) of Fermi GRB 251125B ( GCN 42836) at MASTER-Tunka and MASTER-Kislovodsk. MASTER auto-detection system discovered optical counterpart of this GRB MASTER OT J155558.56+581224.1 with unfiltered m_OT=18.2 at 2025-11-25 20:34:32UT with typical for GRB light curve with decay. https://www.wis-tns.org/object/2025aevl Real time updated cover map and discovered OT position is available here: https://master.sai.msu.ru/site/master2/observ.php?id=3051835 Observations and data analysis will be continued. [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/42838. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...