TITLE: GCN CIRCULAR NUMBER: 23484 SUBJECT: GRB 181201A: Global MASTER-Net prompt optical descovery and afterglow observations DATE: 18/12/02 10:26:59 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, V.Kornilov, D.Kuvshinov, N.Tyurina, P.Balanutsa, A.Kuznetsov, V.V.Chazov, D. Vlasenko Lomonosov Moscow State University, Sternberg Astronomical Institute, Moscow State University A. Tlatov, V.Senik, A.V. Parhomenko, D. Dormidontov Kislovodsk Solar Station of the Pulkovo Observatory K. Ivanov, O. Gres, N.M. Budnev, S. Yazev, O. Chuvalaev, V. Poleshchuk Irkutsk State University V. Yurkov, A. Gabovich, Yu. Sergienko Blagoveschensk Educational State University, Blagoveschensk R. Podesta, Carlos Lopez and F. Podesta Observatorio Astronomico Felix Aguilar (OAFA) Hugo Levato and Carlos Saffe Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE) R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres The Instituto de Astrofisica de Canarias D. Buckley, S. Potter, A. Kniazev, M. Kotze South African Astronomical Observatory MASTER-OAFA robotic telescope (MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the INTEGRAL GRB181201A ((Mereghetti et al., GCN #23469) 10 sec after notice time and 18 sec after trigger time at 2018-12-01 02:40:30 UT. We discovered prompt growing (one mag per minute) optical flash MASTER OT J211711.20-123751.4 (Podesta et al., GCN #23470; Gorbovskoy et al., Atel #12255) at RA,Dec = 21h 17m 11.20s -12d 37m 51.4s Later we observed afterglow at MASTER-Kislovodsk (Lipunov et al., #23476), MASTER-SAAO, MASTER-IAC and MASTER-OAFA against in B,V,R,I and Clear fiters. Observations are continuated. This message can be cited.