Аннотация:MASTER OT J165415.75-540239.27 - SOS emission of the GRB 180728A
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 (Starling et al., GCN #23046; Perri et al., GCN #23049;) 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 XRT error-box (Lipunov et al., GCN Circ #23048; Lipunov et al., GCN Circ #23050) :
MASTER OT J165415.75 -540239.27
RA, DEC = 16h 54m 15.75s , -54d 02m 39.27s
m ~ 14.5 at maximum; 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 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
SOS emission see (Lipunov et al., The Astrophysical Journal, V. 845, Issue 1, article id. 52, 9 pp. (2017))
All follow up observations are required.