TITLE: GCN CIRCULAR NUMBER: 29580 SUBJECT: Integral GRB210227.19: Global MASTER-Net OT detection DATE: 21/02/27 04:56:46 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, V.Kornilov, D.Kuvshinov, N.Tyurina, P.Balanutsa, A.Kuznetsov, A.V. Krylov, I. Gorbunov, D. Vlasenko, F. Balakin Lomonosov Moscow State University, Sternberg Astronomical Institute, Moscow State University R. Podesta, Carlos Lopez and F. Podesta Observatorio Astronomico Felix Aguilar (OAFA) A. Tlatov, V.Senik, A.V. Parhomenko, D. Dormidontov Kislovodsk Solar Station of the Pulkovo Observatory V. Yurkov, A. Gabovich, Yu. Sergienko Blagoveschensk Educational State University, Blagoveschensk K. Ivanov, O. Gres, N.M. Budnev, S.Yazev, O. Chuvalaev, V. Poleshchuk Irkutsk State University 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-OAFA robotic telescope (Global 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 GRB210227.19 42 sec after notice time and 52 sec after trigger time at 2021-02-27 04:34:46 UT. On our 4-th (30s exposure) set , obtained 157 sec after tigger time at 2021-02-27 04:36:30 UT, we found 1 optical transient within Integral error-box (ra=84.7625 dec=17.8122 r=0.05) brighter than 14.5. T-Tmid Date Time Expt. Ra Dec Mag ---------|---------------------|-------|-----------------|-----------------|------- 172 2021-02-27 04:36:30 30 (05h 39m 11.68s , +17d 49m 09.6s) 13.1 The 5-sigma upper limit has been about 14.5mag The message may be cited.