GCN Circular 21181

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

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

D.Buckley
South African Astronomical Observatory


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

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-SAAO  robotic telescope (MASTER-Net: http://observ.pereplet.ru)
located in SAAO was pointed to the  GRB170531.84 25 sec after notice time
and 99 sec after trigger time at 2017-05-31 20:09:15 UT. On our first (20s
exposure)  set we haven`t found optical transient  within SWIFT error-box
(ra=121.258 dec=-14.0328 r=0.05).
The 5-sigma upper limit has been about 15.5mag


The observations made on zenit distance = 84 degrees, galaxy latitude b =
10 degree.
The moon (43 % bright part) is 19 degrees above the horizon. The distance
between  moon and  object is 41
The sun  altitude  is -56.5 degree.


MASTER-IAC robotic telescope (2x4 square degrees, MASTER-Net: 
http://observ.pereplet.ru)  was pointed to the  GRB170531A (Evans et al.,
GCN #21170; Siegel et al. GCN #21172) 895 sec after notice time and 2115 
sec after trigger time on the 2017-05-31 20:42:48 UT.

The observations were made on zenit distance = 74 degrees during 
the twilight. The sun  altitude  was  -9.6 degree.
The moon (43 % bright part) is 58 degrees above the horizon. The distance 
between  moon and  object is 41deg.

On our 5-th (180s exposure)  set we haven`t found optical 
transient  within SWIFT error-box (ra=121.258 dec=-14.0328 r=0.1).
The 5-sigma upper limit m~13.9mag (unfiltered) on the first image and


MASTER-OAFA  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in OAFA was pointed to the  GRB170531.84 15674 sec after notice 
time and 15751 sec after trigger time at 2017-06-01 00:30:03 UT. On our 
first (180s exposure)  set we haven`t found optical transient  within 
Master error-box (ra=121.25 dec=-14.0225 r=0.1).
The 5-sigma upper limit has been about 18mag
The message may be cited.


The observations made on zenit distance = 63 degrees, galaxy latitude b = 
10 degree.
The moon (45 % bright part) is 38 degrees above the horizon. The distance 
between  moon and  object is 43
The sun  altitude  is -35.4 degree.
The object can be observed till 2017-06-01 02:41:37.