TITLE: GCN CIRCULAR NUMBER: 21147 SUBJECT: GRB 170524B: MASTER-OAFA observations DATE: 17/05/26 09:42:12 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs R.Podesta, C.Lopez, F. Podesta Observatorio Astronomico Felix Aguilar (OAFA), National University of San Juan, Argentina H. Levato, C. Saffe Instituto de Ciencias Astronomicas,de la Tierra y del Espacio (ICATE), San Juan, Argentina V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, D.Kuvshinov, A.V.Krylov, I.Gorbunov, P.Balanutsa, A.Kuznetsov, V.V.Chazov, D. Vlasenko Lomonosov Moscow State University, Sternberg Astronomical Institut of MSU K.Ivanov, S.Yazev, N.M.Budnev, O.Gres, O.Chuvalaev, V.A.Poleshchuk, O. Ershova Irkutsk State University V.Yurkov, Yu.Sergienko Blagoveschensk Educational State University, Blagoveschensk A. Tlatov, V.Senik, A.V. Parhomenko, D. Dormidontov Kislovodsk Solar Station of the Pulkovo Observatory D.Buckley, S. Potter, A.Kniazev, M.Kotze South African Astronomical Observatory R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres The Instituto de Astrofisica de Canarias MASTER robotic telescope (6 square degrees) located in OAFA was pointed to the GRB170525B (Barthelmy et al., GCN #21142) 15191 sec after notice time and 43294 sec after trigger time at 2017-05-25 22:42:14 UT. On our first (180s exposure) set we haven`t found optical transient within Master error-box (ra=90.8625 dec=-17.0861 r=0.1). The 5-sigma upper limit has been about 18.3 mag There is no OT at added images brighter 19.9 at Swift XRT position (Barthelmy et al., GCN #21142; Evans, GCN #21144 ). The observations made on zenit distance = 59 degrees, galaxy latitude b = -18 degree. The moon ( 0 % bright part) below the horizon (The altitude of the Moon is -8 degree ). Observations started at twilight. The sun altitude is -12.7 degree. The object can be observed till 2017-05-26 01:12:20 The message may be cited.