TITLE: GCN CIRCULAR NUMBER: 17778 SUBJECT: GRB 150428A: MASTER-net early optical observation DATE: 15/04/28 15:19:00 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs D.Buckley, S. Potter, A.Kniazev, M.Kotze South African Astronomical Observatory E. Gorbovskoy, V. Lipunov, N.Tyurina, V.Kornilov, P.Balanutsa, A.Kuznetsov, D.Kuvshinov, Lomonosov Moscow State University, Sternberg Astronomical Institute 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 GRB150428A (Page et al, GCN 17765) 28 sec after notice time and 90 sec after trigger time at 2015-04-28 01:32:10 UT in two polarizations. On our first single and coadd images we haven`t found optical transient within SWIFT error-box . The observations made on a high zenith distance ~ 80 d. We obtain a followin upper limits: Date start T_s-T_tr T_m-T_trig Expt. Limit Coadd (mean_time) 01:32:10.9 90 100 20 16.0 no 01:32:43.2 122 132 20 16.0 no 01:33:14.7 153 168 30 16.4 no 01:33:14.7 153 224 120 17.0 3 01:33:14.7 153 583 770 18.5 9 Also, we can not confirm Danish 1.56m OT (Andersen et. al GCN 17771), because they do not see it on our images with upper limits specified above. The message may be cited.