TITLE: GCN CIRCULAR NUMBER: 16312 SUBJECT: GRB 140521A: MASTER optical observations DATE: 14/05/21 22:28:09 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Vladimirov, P.Balanutsa, E. Gorbovskoy, V. Lipunov, V.Kornilov, D.Kuvshinov, A.Belinski, N.Tyurina, N.Shatskiy, D.Zimnukhov, A.Kuznetsov, V.V.Chazov, D.Denisenko, A.Sankovich, A. Krylov, M.Pruzhinskaya Lomonosov Moscow State University, Sternberg Astronomical Institute, Moscow 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 K.Ivanov, S.Yazev, N.M.Budnev, O.Gres, O.Chuvalaev, V.A.Poleshchuk Irkutsk State University 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 Vostryakovo (Alexander Krylov Observatory) was pointed to the GRB140521A 4553 sec after trigger time at 2014-05-21 18:50:11 directly after sunset. We haven`t found optical transient within SWIFT error-box (Troja et. al GCN 16311) on single and coadd images. In table 1 the images upper limits are provided. Table 1. ------- T_start Exptime T-T_mead T-T_start T-T_stop Filter mlimit Coadd 2014-05-21 18:50:11 15 4561 4553 4568 C 14.5 1* 2014-05-21 19:10:18 600 6531 5760 7302 C 18.0 10 2014-05-21 19:10:18 1020 7210 5760 8659 C 18.8 17 2014-05-21 19:38:52 600 8067 7474 8659 C 18.7 10 2014-05-21 20:07:53 1200 10390 9215 11566 C 19.4 20 ----------------------------------------------------------------------------------- * First image with stars on bright evening sky. C is our white (clear) band which is well described by a parity 0.8R+0.2B (USNO B1). T is a GRB trigger time. Another two MASTER II robotic telescope located in Kislovodsk and Blagoveschensk was pointed to the GRB140521A 21 sec after notice time and 36 sec after trigger time at 2014-05-21 17:34:54 UT. But observations were spoiled due to bad weather condition. We have a set of images from that observatories with different exposures from 10 to 180 and formal upper limit from 13 to 16 during first hour after the burst. However bad quality of images (due to wind and clouds) don't allow to carry out transient search. The message may be cited.