TITLE: GCN CIRCULAR NUMBER: 23359 SUBJECT: GRB 181020A: Global MASTER Net OT observations DATE: 18/10/21 18:05:37 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 D. Buckley, S. Potter, A. Kniazev, M. Kotze South African Astronomical Observatory 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 MASTER-SAAO robotic telescope (MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was starting survey on the SWIFT GRB181020.79 error-box (ra=00 55 55.78 dec=-47 22 52 r=0.05; Moss et all., GCN #23349; Axelsson et al., Fermi LAT, GCN #23350) 7550 sec after notice time and 7572 sec after trigger time at 2018-10-20 21:06:45 UT. The delay connected with weather condition around trigeer time. The 5-sigma upper limit on our first (540s exposure) coadd set is about 19.5 mag We see possible nonmonotonic behaviour OT detected UVOT ( Moss et all., GCN #23349;). More accurate (handmade) reduction will be coming. The automatic OT LC is available at http://observ.pereplet.ru/images/GRB181020A_LC.jpg The galactic latitude b = -70 deg., longitude l = 300 deg. The observations made on zenit distance = 16 deg.The moon (85 % bright part) is 60 deg. above the horizon. The distance between moon and object is 45 degrees. The sun altitude is -43.7 deg. The object can be observed till sunrise at 2018-10-21 03:49:44 This message may be cited.