GCN Circular 21391

V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, D.Kuvshinov, A.V.Krylov,
I.Gorbunov, P.Balanutsa, A.Kuznetsov, V.V.Chazov, D. Vlasenko
Lomonosov Moscow State University, Sternberg Astronomical Institut of MSU

R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres
The Instituto de Astrofisica de Canarias

R.Podesta, C.Lopez, F. Podesta Observatorio Astronomico Felix Aguilar (OAFA),
National University of San Juan, Argentina

H. Levato, C. Saffe
Instituto de Ciencias Astronomicas,de la Tierra y del Espacio (ICATE),
San Juan, Argentina

O.Gres, K.Ivanov, S.Yazev, N.M.Budnev, O.Gres, O.Chuvalaev, 
V.A.Poleshchuk,
Irkutsk State University

V.Yurkov, Yu.Sergienko
Blagoveschensk Educational State University, Blagoveschensk

A. Tlatov, V.Senik, A.V. Parhomenko, D. Dormidontov
Kislovodsk Solar Station of the Pulkovo Observatory

D.Buckley, S. Potter, A.Kniazev, M.Kotze
South African Astronomical Observatory


MASTER II  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in IAC was pointed to the  GRB170728B (Cenko et al., GCN Circ.
#21371)  28 sec after notice time 
and 39 sec after trigger time at 2017-07-28 23:04:01 UT. On our first (10s 
exposure)  set we  found optical transient   within  SWIFT XRT error-box ( 
D'Elia et al., GCN #21376; ) in two polarizations! 
The 5-sigma upper limit has been about 16.9 mag
We 100% found faiding OT  on  first 10 minutes  images with m ~ 16.5  up 
to 18 mag.

RA, DEC  = 15h 51m 55s.5 , +70d 7m 19s.3
Error = +- 1.4 arcsec

The faiding OT may be coincide with D'Avanzo et al. position  (GCN 
#21372) and Heintz et al., (GCN #21374) and Izzo et al., (GCN #21381) and

The observations made on zenit distance = 47 degrees, galaxy latitude b = 
40 degree.
The moon (34 % bright part) is  8 degrees above the horizon. The distance 
between  moon and  object is 78
The sun  altitude  is -33.7 degree.
The error box can be observed till sunrise at 2017-07-29 06:25:17.

The message may be cited.