TITLE: GCN CIRCULAR NUMBER: 23109 SUBJECT: GRB180809B: MASTER OT observation DATE: 18/08/10 00:26:43 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, N.Tiurina, E. Gorbovskoy, V.Kornilov, A.Kuznetsov, V.Chazov, I. Gorbunov, D.Zimnukhov, D.Kuvshinov, P.Balanutsa, V.Vladimirov, D. Vlasenko Lomonosov Moscow State University,SAI R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres The Instituto de Astrofisica de Canarias (IAC) D. Buckley, South African Astronomical Observatory (SAAO) A. Tlatov, V.Senik, D. Dormidontov Kislovodsk Solar Station of the Pulkovo Observatory R. Podesta, F. Podesta, C. Lopez, C.Francile Observatorio Astronomico Felix Aguilar (OAFA) H.Levato, Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE) O. Gres, N.M.Budnev , Yu.Ishmuhametova Irkutsk State University (ISU) A. Gabovich, V. Yurkov, Yu. Sergienko Blagoveschensk Educational State University (BSPU) 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 pointed to the GRB180809B(Moss et al. GCN 23105) 16 sec after notice time and 42 sec after trigger time at 2018-08-09 20:30:40 UT. On our 3-th (20s exposure) set , obtained 101 sec after tigger time at 2018-08-09 20:31:39 UT, we found 1 optical transient within SWIFT error-box T-Tmid Date Time Expt. Ra Dec mag ---------|---------------------|-------|-----------------|-----------------|------- 111 2018-08-09 20:31:39 20 (19h 58m 48.0s , -15d 17m 57.1s) 16.87 also detected by Swift UVOT (Moss et al. GCN 23105) The 5-sigma upper limit has been about 17.4mag The message may be cited.