TITLE: GCN CIRCULAR NUMBER: 26047 SUBJECT: Swift GRB191020.81: Global MASTER-Net OT detection DATE: 19/10/20 19:47:21 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 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-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 GRB191020.81 20 sec after notice time and 297 sec after trigger time at 2019-10-20 19:25:00 UT. On our 6-th (180s exposure) set , obtained 925 sec after tigger time at 2019-10-20 19:35:29 UT, we found 1 optical transient within Swift error-box (ra=339.992 dec=-17.3211 r=0.1) brighter than 18.55. T-Tmid Date Time Expt. Ra Dec Mag ---------|---------------------|-------|-----------------|-----------------|------- 1015 2019-10-20 19:35:29 180 (22h 39m 57.886s , -17d 24m 35.54s) 15.97 The OT has irregular early time behaviour since 1139 till 1532.5 seconds after the trigger. The 5-sigma upper limit has been about 18.55mag The message may be cited.