TITLE: GCN CIRCULAR NUMBER: 42346 SUBJECT: GRB 251018A: MASTER OT detection DATE: 25/10/18 07:51:23 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru> V. Lipunov, I.Panchenko, A.Kuznetsov, G.Antipov, P.Balanutsa, E.Gorbovskoy, K.Zhirkov, N.Tiurina, A.Sankovich, Ya.Kechin, Yu. Tselik, M.Shilova, A.Chasovnikov, V.Topolev, V.Senik, D.Vlasenko, V.Shumkov, K.Vetrov, P.Rudominskaya (Lomonosov MSU, SAI, Moscow), R.Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA, San Juan Uni.,Argentina); D.Buckley, (SAAO, South Africa) O.Gress, N.Budnev (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) The MASTER-OAFA robotic telescope of MASTER Global Robotic Net [1-4] started Fermi (GCN 42342) and Swift GRB 251018A (Gupta et al. GCN 42343, Trigger time 2025-10-18 03:12:02UT) 105s after notice time (141s after trigger time) at 2025-10-18 03:14:24 UT (Lipunov et al. GCN 42344, cover map and OT https://master.sai.msu.ru/site/master2/observ.php?id=3017251 There is MASTER OT J184810.01-370141.6,detected since first image (03:14:24) with m_OT=16.5 at 2025-10-18 03:16:46 (unfiltered, automatically calculated) This OT was discovered by Swift-UVOT (Gupta et al. GCN 42343) and observed by TRT (S.Y.Fu et al. GCN 42345) at the same time. Observation and reduction 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/42346. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...