TITLE: GCN CIRCULAR NUMBER: 43619 SUBJECT: GRB 260204A : MASTER Global robotic net optical observations DATE: 26/02/05 01:13:33 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru> V.M.Lipunov (Lomonosov MSU), O.A.Gress, N.M.Budnev (ISU), V.A.Senik, I.Panchenko, P.Balanutsa, A.Kuznetsov, E.Gorbovskoy, G.Antipov, N. Tiurina, Ya.Kechin,A.Chasovnikov, D.Vlasenko, I.Ionov,Yu.Tselik(Lomonosov MSU), 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), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino, J.Martinez, A.R.Corella, J.G. Tanori, L. F. Villalobos, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico) V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias,Spain) At alert and notice time the error-box of SVOM GRB 260204A (Pillas et al. GCN 43613, also by Fermi-GBM GCN 43618; in optic observed by LCO (Turpin et al. GCN 43616), GOTO (Kumar et al. GCN 43617)) altitude was -8deg at MASTER-Tunka (the nearest MASTER for observation). So we started observe it several hours later. MASTER-Tunka robotic telescope [1-3] located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the SVOM GRB260204A (trigger No 1770219433,13h 40m 56.04s , +01d 58m 50.2s, R=0.0662) errorbox 12301 sec after notice time (13245 sec after trigger time) at 2026-02-04 19:17:57 UT, with upper limit up to 18.1 mag at single images and 19.9 at summary. MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the SVOM GRB 260204A errorbox 16703 sec after notice time and 17647 sec after trigger time at 2026-02-04 20:31:20 UT, with upper limit up to 17.1 mag. The observations began at zenith distance = 81 deg. The sun altitude was -60.8 deg. The galactic latitude b = 62 deg., longitude l = 331 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3122418 Observation and reduction will continue. [1] Lipunov et al. 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html [2] Lipunov et al. 2022, Universe, 8, id.271 [3] Lipunov et al. 2023, Astronomy Reports, 67, p.S140 View this GCN Circular online at https://gcn.nasa.gov/circulars/43619. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...