TITLE: GCN CIRCULAR NUMBER: 19838 SUBJECT: Short GRB 160821B: MASTER early optical observations DATE: 16/08/22 09:08:42 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs R. Rebolo, M. Serra-Ricart, G. Israelian, N. Lodieu The Instituto de Astrofisica de Canarias V. Lipunov, N.Tyurina, E. Gorbovskoy, V.Kornilov, P.Balanutsa, A.Kuznetsov, D.Kuvshinov Lomonosov Moscow State University, Sternberg Astronomical Institute K.Ivanov, O.Gres, N.M.Budnev, S.Yazev, Irkutsk State University D.Buckley, S. Potter, A.Kniazev, M.Kotze South African Astronomical Observatory A. Tlatov, V.Senik, D. Dormidontov, A.Parkhomenko Kislovodsk Solar Station of the Pulkovo Observatory V.Yurkov, Yu.Sergienko, A.Gabovich Blagoveschensk Educational State University, Blagoveschensk Hugo Levato, Carlos Saffe Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE) R.Podesta, C.Mallamaci, C.Lopez, F. Podesta Observatorio Astronomico Felix Aguilar (OAFA) MASTER-IAC twin robotic telescope (MASTER-Net: http://observ.pereplet.ru, online view http://161.72.133.2/) located in IAC (Tenerife, Spain) was pointed to the GRB160821B (Siegel et al., GCN 19833) 34 sec after notice time and 53 sec after trigger time at 2016-08-21 22:30:06 UT. The alert coordinates altitude was 55 deg. at MASTER-IAC, the Sun altitude was -35d, the Moon distance is 90 degrees. On our first (10s exposure - two images in perpendicular polarizations) set we not found optical transient within SWIFT error-box (Evans et al., GCN 19837) and at NOT OT position (Xu et al., GCN 19834) brighter then 16.6. The resuts of the first 5 minutes observations are: Id Pro.type UT Exp.time Limit Filt. Tube. (Start) (s) (5sigma) (polarizator) 285342 Alert 22:30:06 10 16.6 P- WEST 285343 Alert 22:30:06 10 16.6 P| EAST 285342 Alert 22:30:06 10 16.6 P- WEST 285345 Alert 22:30:43 20 17.1 P| EAST 285346 Alert 22:31:24 30 17.1 P- WEST 285347 Alert 22:31:24 30 16.6 P| EAST 285348 Alert 22:32:08 30 16.6 P- WEST 285349 Alert 22:32:08 30 16.6 P| EAST 285350 Alert 22:32:50 40 17.2 P- WEST 285351 Alert 22:32:50 40 17.0 P| EAST 285352 Alert 22:33:43 50 17.3 P- WEST 285353 Alert 22:33:43 50 17.2 P| EAST 285355 Alert 22:34:46 70 17.5 P- WEST 285354 Alert 22:34:46 70 0.0 P| EAST The limit of the coadded west tube images is 18.7 with start time 22:30:06, finish time = 22:35:56 and mean time = 22:33:01 UT. The message may be cited.