TITLE: GCN CIRCULAR NUMBER: 42395 SUBJECT: GRB 251022A: MASTER OT detection DATE: 25/10/23 12:43:30 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs lipunov@xray.sai.msu.ru

V. Lipunov, I.Panchenko, A.Kuznetsov, O.Gress, G.Antipov, P.Balanutsa, 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, M.Shilova(Lomonosov MSU, SAI, Moscow), R.Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA, San Juan Uni.,Argentina); D.Buckley (SAAO, South Africa), 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)

MASTER Global Robotic Net [1-4] started Fermi GRB 251022A (GCNC 42380, Ttrigger=2025-10-22 22:34:15.26 ,GBM_notice=2025-10-22 22:43:43, LAT_notice=2025-10-23 03:04:17UT, LAT_center=04 21 31.18 -19 18 35.6 +-0.32deg (Di Lalla et al. GCN 42384) at MASTER-SAAO and MASTER-OAFA (Lipunov et al. GCNC 42381) 13s after LAT_notice_time (16215s after trigger time)

There is MASTER OT J042159.34-185510.4 since 2025-10-23 03:04:54UT with unfiltered m_OT=18.0. This OT can be on MASTER very wide field images at earlier images in MASTER-Tunka, that started GBM error-filed observations in alert mode, the reduction will be continued.

This OT was discovered by GOTO (O'Neill et al. GCNC 42386) and also observed by DDOTI (Becerra et al. GCNC 42394)

We analyzed SWIFT XRT candidates (Evans et al. GCNC42382, https://www.swift.ac.uk/xrt_products/TILED_GRB00139/ ) The first one ( 04h 20m 03.25s -19° 19′ 50.1″) coincides with QSO (UV/GALEX, xray/eROSITA detection) in 2.8" from center of SWIFT error-box.

The second one (04 20 23.62 -19 15 45.2) coincides with second QSO (see VIZIER for full information) in 2.5" from the center of Swift error-box.

Both has complicated light curves without significant details at 23 oct 2025.

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

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