[vsnet-grb-info 16499] GRB 150428B: MASTER-net prompt optical observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17780
SUBJECT: GRB 150428B: MASTER-net prompt optical observation
DATE:    15/04/28 15:33:45 GMT
FROM:    Vladimir Lipunov at Moscow State U/Krylov Obs  <lipunov at xray.sai.msu.ru>

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

E. Gorbovskoy, V. Lipunov,  N.Tyurina, V.Kornilov, P.Balanutsa, A.Kuznetsov, 
D.Kuvshinov,
Lomonosov Moscow State University, Sternberg Astronomical Institute

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

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

V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov
Blagoveschensk Educational State University, Blagoveschensk

V.Krushinski, I.Zalozhnih,  A. Popov
Ural Federal University, Kourovka

Hugo Levato and Carlos Saffe
Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

Claudio Mallamaci, Carlos Lopez and Federico Podest
Observatorio Astronomico Felix Aguilar (OAFA)

MASTER II  robotic telescope (MASTER-SAAO: http://observ.pereplet.ru) 
located in SAAO was pointed to the  GRB150428B 24 sec after notice time 
and 59 sec after trigger time at 2015-04-28 03:13:03 UT in two 
polarizations. On our first (10s exposure)  set we haven`t found optical 
transient  within SWIFT BAT (Page et. al GCN 17766) and XRT (Beardmore et 
al. GCN 17773) error-boxes .
We have 3x2 images during Gamma Ray activity (see Page et al., GCN 17777) 
in two polarizations.
So our observations is prompt observations.
We obtain a followin upper limits on single and coadd images:

Date start  T_start -T_trig  T_mid-T_trig  Expt.  Limit Coadd

03:13:03.3        59             64         10    16.5   no
03:13:03.3        59             97         50    17.4    3
03:13:03.3        59            529        810    19.3   12


Data analysis was hampered by a high density of stars in the error box. 
XRT position covered by  bright (~15m) star USNO B1 0941-0468603.



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