TITLE: GCN CIRCULAR NUMBER: 17680 SUBJECT: GRB 150403A: MASTER-net optical observation DATE: 15/04/06 17:24:35 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs E. Gorbovskoy, V. Lipunov, N.Tyurina, V.Kornilov, P.Balanutsa, A.Kuznetsov, D.Kuvshinov, Lomonosov Moscow State University, Sternberg Astronomical Institute D.Buckley, S. Potter, A.Kniazev, M.Kotze South African Astronomical Observatory K.Ivanov, S.Yazev, N.M.Budnev, O.Gres, O.Chuvalaev, V.A.Poleshchuk Irkutsk State University A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Sennik Kislovodsk Solar Station of the Pulkovo Observatory V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov Blagoveschensk Educational State University, Blagoveschensk V.Krushinski, I.Zalozhnih, A. Popov Ural Federal University, Kourovka Hugo Levato and Carlos Saffe Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE) Claudio Mallamaci, Carlos Lopez and Federico Podest Observatorio Astronomico Felix Aguilar (OAFA) MASTER II robotic telescope (MASTER-Net: http://observ.pereplet.ru) located in SAAO was pointed to the GRB150403A (Lien et al. GCN 17665) 20418 sec after notice time and 20434 sec (5.7h) after trigger time at 2015-04-04 03:34:51 UT immediately after suitable weather condition came, in automatic mode. Observation lasted about 30 minutes, until the weather became bad again. We detect a faint OT on a Swift UVOT position (Kuin et al. GCN17673). The estimated unfiltered magnitude is: Date time_start T0-Tmid[s] Expt.[s] Mag Coadd 2015-04-04 03:34:51.49 20840 720 19.2 4 Our unfiltered band is well described by a parity 0.8R+0.2B (USNO B1). The message may be cited.