TITLE: GCN CIRCULAR NUMBER: 26596 SUBJECT: Swift GRB191227A: Global MASTER-Net OT detection DATE: 19/12/27 02:46:31 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, V.Kornilov, D.Kuvshinov, N.Tyurina, P.Balanutsa, A.Kuznetsov, 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) D. Buckley, S. Potter, A. Kniazev, M. Kotze South African Astronomical Observatory K. Ivanov, O. Gres, N.M. Budnev, S. Yazev, O. Chuvalaev, V. Poleshchuk Irkutsk State University 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 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 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 GRB191227.07 31 sec after notice time and 51 sec after trigger time at 2019-12-27 01:40:28 UT. On our first (10s exposure) set we found 1 optical transient within Swift error-box (ra=319.167 dec=-16.7033 r=0.05) brighter than 15.3. T-Tmid Date Time Expt. Ra Dec Mag ---------|---------------------|-------|-----------------|-----------------|------- 56 2019-12-27 01:40:28 10 (21h 16m 37.28s , -16d 43m 33.5s) 14.4 The 5-sigma upper limit has been about 15.3mag The message may be cited. The OT has irregular early time behaviour since 51.1 till 501.5 seconds after the trigger. The galactic latitude b = -40 deg., longitude l = 34 deg. The observations made on zenith distance = 83 deg.The moon ( 1 % bright part) below the horizon (The altitude of the Moon is -14 deg. ). The sun altitude is -20.6 deg.