TITLE: GCN CIRCULAR NUMBER: 23050 SUBJECT: GRB 180728A: MASTER OT J165415.75-540239.27 is the Optical Counterpart of GRB DATE: 18/07/28 19:35:21 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, N.Tiurina, D.Vlasenko, V.Kornilov, A.Kuznetsov, V.Chazov, I. Gorbunov, D.Zimnukhov, D.Kuvshinov, P.Balanutsa, V.Vladimirov, Lomonosov Moscow State University,SAI D. Buckley, South African Astronomical Observatory (SAAO) R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres The Instituto de Astrofisica de Canarias (IAC) 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 detected new optical object (Lipunov et al., GCN Circ #23048) MASTER OT J165415.75-540239.27 at Swift XRT position (Starling et al., GCN #23046; Perri et al., GCN #23049;): RA, DEC = 16h 54m 15.75s , -54d 02m 39.27s Error ~1 arcsec We see a gradual attenuation of the OT on an automatic light curve. Thus, the transient is an optical counterpart of the gamma-ray burst GRB 180728A. The automatic light curve is available at http://observ.pereplet.ru/images/MASTER_OT_J165415.75-540239.27.jpg The message may be cited.