TITLE: GCN CIRCULAR NUMBER: 23048 SUBJECT: GRB 180728A: MASTER OT (= new object) detection DATE: 18/07/28 18:33:41 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 pointed to the GRB180728A 22 sec after notice time and 38 sec after trigger time at 2018-07-28 17:29:38 UT in two polarizations. On our first (10s exposure) set we found new optical object (transient) within SWIFT error-box (ra=253.567 dec=-54.0308 r=0.05) : MASTER OT J165415.75 -540239.27 RA, DEC = 16h 54m 15.75s , -54d 02m 39.27s m ~ 14.5 We see a surprising automatic light curve when the source has risen to constant magnitude during first ~30 minutes! The observations made on zenit distance = 28 degrees, galaxy latitude b = -7 degree. The moon (99 % bright part) is 11 degrees above the horizon. The distance between moon and object is 61 The sun altitude is -19.8 degree. The object can be observed till 2018-07-29 05:17:09 The message may be cited.