TITLE: GCN CIRCULAR NUMBER: 21449 SUBJECT: GRB 170810A: MASTER-NET very bright OT detection DATE: 17/08/10 22:17:00 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres The Instituto de Astrofisica de Canarias V. Lipunov, E. Gorbovskoy, V.Kornilov, D.Kuvshinov, N.Tyurina, P.Balanutsa, A.Kuznetsov, V.V.Chazov, D. Vlasenko Lomonosov Moscow State University, Sternberg Astronomical Institute, Moscow State University K. Ivanov, O. Gres, N.M. Budnev, S. Yazev, O. Chuvalaev, V. Poleshchuk Irkutsk State University A. Tlatov, V.Senik, A.V. Parhomenko, D. Dormidontov Kislovodsk Solar Station of the Pulkovo Observatory V. Yurkov, A. Gabovich, Yu. Sergienko Blagoveschensk Educational State University, Blagoveschensk D. Buckley, S. Potter, A. Kniazev, M. Kotze South African Astronomical Observatory R. Podesta, Carlos Lopez and F. Podesta Observatorio Astronomico Felix Aguilar (OAFA) Hugo Levato and Carlos Saffe Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE) MASTER II robotic telescope (MASTER-Net: http://observ.pereplet.ru) located in IAC was pointed to the GRB170810A 25 sec after notice time and 45 sec after trigger time at 2017-08-10 22:02:26 UT. On our first (10s exposure) set we found very bright OT. Mag: 11.258 Ra: 187.938775 Dec: 3.660714 The message may be cited. The observations made on zenit distance = 85 degrees, galaxy latitude b = 66 degree. The moon (90 % bright part) is 4 degrees above the horizon. The distance between moon and object is 169 The sun altitude is -27.0 degree. The object can be observed till sunrise at 2017-08-11 06:32:12.