TITLE: GCN CIRCULAR NUMBER: 42930 SUBJECT: Swift GRB 251201B : MASTER optical counterpart detection DATE: 25/12/01 23:18:16 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru> D.Buckley (SAAO), V.M. Lipunov (Lomonosov MSU), A.Kuznetsov, I.Panchenko, G.Antipov, P.Balanutsa, K.Zhirkov, V.Senik, N. Tiurina, Ya.Kechin, A.Chasovnikov, D.Vlasenko, E.Gorbovskoy, Yu.Tselik(Lomonosov MSU, SAI, Moscow), O.A.Gress, N.M.Budnev, O.Ershova (Irkutsk State University), R. Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA, San Juan Uni.,Argentina); 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-SAAO robotic telescope of MASTER Global Robotic Net (Lipunov et al. [1-4], http://observ.pereplet.ru ), started Swift GRB 251201B (Moss et al GCN 42924, Osborne et al. GCN 42927) inspect at 2025-12-01 22:00:57 UT (20067s after trigger time), Lipunov et al. GCN 42929 There is optical counterpart MASTER OT J002534.28-441352.2 at Swift UVOT position (Moss et al. GCN 42924) with unfiltered m_OT~20.4m at summary image at 22:00:57 UT (420s exposition, mlim=21m). Real time updated cover map and OT position are available here: https://master.sai.msu.ru/site/master2/observ.php?id=3054567 Observation and reduction will continue. [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/42930. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...