TITLE: GCN CIRCULAR NUMBER: 23065 SUBJECT: GRB 180728B: MASTER optical observations short GRB IPN error box DATE: 18/07/31 06:56:36 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, P.Balanutsa, N.Tiurina, D.Vlasenko, V.Kornilov, A.Kuznetsov, V.Chazov, I. Gorbunov, D.Zimnukhov, D.Kuvshinov, V.Vladimirov, Lomonosov Moscow State University,SAI D.Svinkin (Ioffe Institute, StPetersburg, Russia) 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) located in SAAO was starting survey on the IPN GRB180728B error-box (Svinkin et al., GCN Circ #23056; Hamburg et al., GCN Circ #23057) 14269 sec after notice time and 70698 sec after trigger time at 2018-07-29 16:48:15 UT. The 5-sigma upper limit on our first (180s exposure) set is about 18mag. The typical limit of coadded images is about 20 mag. We marginally found one candidate to uncataloged object source near PGC052927 galaxy: MASTER OT J144922.8+164418.2 RA,DEC = 14h 49m 22.8s +16d 44' 18.2" error = 0.7 arcsec mag = 19.7; The offset from galaxy is 10.8W and 22.2N arcsec. ==================================================================== The observations made on zenit distance = 50 degrees, galactic latitude b = 61 degree. The moon (97 % bright part) below the horizon (The altitude of the Moon is -8 deg. Observations started at twilight. The sun altitude is -11.1 deg. The object can be observed till sunrise at 2018-07-30 05:26:48. The covered map is available at http://master.sai.msu.ru/static//IPN/db/GRB180728.88/img/ligo_master_2018-07-30-16-09-11.eb.zoom.1.png We reobserved possible transient on the next night starting 2018-07-30 16:57:46 UT. We do not find the object brighter than 20.5 .