TITLE: GCN CIRCULAR NUMBER: 30904 SUBJECT: Swift GRB211001.03: Global MASTER-Net OT detection DATE: 21/10/01 00:50:48 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru> 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) 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-Tavrida robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the GRB211001.03 27 sec after notice time and 41 sec after trigger time at 2021-10-01 00:44:01 UT. On our 3-th (20s exposure) set , obtained 100 sec after tigger time at 2021-10-01 00:44:59 UT, we found 1 optical transient within Swift error-box (ra=71.4667 dec=12.0397 r=0.05) brighter than 14.6. T-Tmid Date Time Expt. Ra Dec Mag ---------|---------------------|-------|-----------------|-----------------|------- 110 2021-10-01 00:44:59 20 (04h 46m 00.28s , +12d 02m 15.1s) 14.2 The 5-sigma upper limit has been about 14.6mag The message may be cited.