MASTER OT Detection at SWIFT XRT Position

ATel #11895; P. Balanutsa, V. Lipunov, V. Kornilov, E. Gorbovskoy, N. Tiurina, O. Gress, A. Gabovich, I. Gorbunov, V. Senik, V. Vladimirov, D. Vlasenko, D. Kuvshinov (Lomonosov MSU), D. Buckley (SAAO)
on 28 Jul 2018; 19:58 UT
Credential Certification: Nataly Tyurina (tiurina@sai.msu.ru)

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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.

MASTER Global Robotic Net