GCN Circular 21173

V. Lipunov, V.Kornilov, N.Tyurina, E.Gorbovskoy, 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

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

N.M.Budnev, O.Gres, O. Ershova 
Irkutsk State University

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

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

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


MASTER-Kislovodsk robotic telescope (2x4 square degrees, MASTER-Net: 
http://observ.pereplet.ru)  was pointed to the  GRB170531B (Evans et al.,
GCN #21171)  12 sec after notice time and 452 sec after trigger 
time on 2017-05-31 22:09:44 UT.
There is marginally seen optical transient at the position 19h 07m 32.03s 
-16d 25' 10.4" with m_OT~19.0+-0.5

The 5-sigma upper limit is about 18.5mag
The message may be cited.


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The observations made on zenit distance = 64 degrees, galaxy latitude b = -11 degree.
The moon (44 % bright part) below the horizon (The Moon altitude is -6 degree).
The sun  altitude  is -22.7 degree.
The object can be observed till sunrise at 2017-06-01 01:30:50 .



The message may be cited.