TITLE: GCN CIRCULAR NUMBER: 43095 SUBJECT: GRB 251214B : MASTER optical afterglow detection DATE: 25/12/14 12:55:36 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs lipunov@xray.sai.msu.ru

O.A.Gress, N.M.Budnev (ISU), V.M.Lipunov, P.Balanutsa, I.Panchenko, A.Kuznetsov, E.Gorbovskoy, G.Antipov, N. Tiurina, Ya.Kechin,A.Chasovnikov, D.Vlasenko, V.Shumkov, I.Ionov, Yu.Tselik(Lomonosov MSU, SAI, Moscow), R.Mirgazov, A.Diachok, O.Ershova (Irkutsk State University), R. Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA, San JuanUni.,Argentina); D.Buckley (SAAO), 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 OT J220050.55-090945.8 detection

MASTER-Tunka robotic telescope of MASTER Global Robotic Net (Lipunov et al. [1-4], http://observ.pereplet.ru ), started Fermi (GCN 43088) and Swift (GCN 43089) GRB 251214B error-box observations after sunset at 2025-12-14 10:20:46 UT (Lipunov et al. GCN 43091, cover map https://master.sai.msu.ru/site/master2/event.php?id=3070779 )

MASTER auto-detection system found optical afterglow at summary images MASTER OT J220050.55-090945.8 , discovered by Swift (Eyles-Ferris et al. GCN 430089) and also observed by SVOM (Zhe Kang et al. GCN 43093) with unfiltered m_OT=19.5m at 2025-12-14 10:49:16UT.

There is SDSS galaxy (poss.host) in 0.067" in VIZIER database with z_phot=0.6634

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

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