TITLE: GCN CIRCULAR NUMBER: 43978 SUBJECT: GRB 260310A / AT2026fgk : MASTER OT rebrightening during 7h observations DATE: 26/03/13 02:18:22 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru> V.Lipunov (Lomonosov MSU), N.Budnev, O.Gress (ISU), A.Kuznetsov, I.Panchenko, P.Balanutsa, G.Antipov, E.Gorbovskoy, N.Tiurina, Ya.Kechin, V.Senik, A.Chasovnikov, M.Shilova,V.Topolev, D.Vlasenko, A.Sankovich, Yu.Tselik (Lomonosov MSU), D.Svinkin (Ioffe Institute), M.J. Segura, C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,A.R.Corella, J.Tanori, L. Villalobos, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) MASTER Global Robotic Net [1-4] started Fermi GRB 260310A observations (Fermi team GCN 43951) at MASTER-Tunka robotic telescope at 2026-03-10 16:01:36 UT (Lipunov et al. GCN 43954) Optical transient AT2026fgk, discovered by GOTO at 2026-03-10 05:14:30.624 (TNSC 1001, https://www.wis-tns.org/object/2026fgk ) was detected as MASTER OT J143716.19+715031.2 at our images at 2026-03-12 13:46:11UT with m_unfiltered~18.3. This OT was observed at 400 images with rebrigtening detection to 17.2 at 2026-03-12 21:02:59 UT. 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 et al. 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/43978. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...