TITLE: GCN CIRCULAR NUMBER: 17518 SUBJECT: GRB 150301B: MASTER early OT detection DATE: 15/03/01 20:51:41 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, V.Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, V.V.Chazov, D.Kuvshinov, Lomonosov Moscow State University, Sternberg Astronomical Institute, Moscow State University V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov Blagoveschensk Educational State University, Blagoveschensk A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Sennik Kislovodsk Solar Station of the Pulkovo Observatory V.Krushinsky, I.Zalozhnih, A. Popov Ural Federal University, Yekaterinburg, 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 GRB150301.82 (Lien et al, GCN 17515) 60 sec after notice time and 79 sec after trigger time at 2015-03-01 19:39:23 UT in two polarizations. On our first (10s exposure) set we found 1 optical transient within SWIFT error-box (ra=05 56 37 dec=-57 58 35 r=0.050000). T_start RA DEC Exp unfiltered s magnitude 2015-03-01 19:39:23 79.0 05h 56m 39.94s -57d 58m 10.0s 15.3 The error is about 0.5 arcsec. This position is coincidet with UVOT data. We detected OT before maximum brightness. The 5-sigma upper limit has been about 16.8 mag . The telegram is generated automatically. We have number of the images after maximum in two polarizations. The reduction is continuated. The message may be cited.