GCN Circular 20381

V.M.  Lipunov, N.Tyurina, E. Gorbovskoy, V.G. Kornilov, P.Balanutsa, 
A.Kuznetsov, V.Shumkov, M.I.Panchenko 
Lomonosov Moscow State University, Sternberg Astronomical Institute

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

R. Rebolo, M. Serra-Ricart, G. Israelian, N.Lodiu
The Instituto de Astrofisica de Canarias

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

N.M. Budnev, O. Gress, K. Ivanov
Irkutsk State University

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


Global MASTER Net was starting observations of the LIGO/Virgo G268556 
error field at 2017-01-04 15:46:07 UT during regular sky survey up to 20 
unfiltered magnitude.

After received alert circular (Shawhan et al.,20364) we started 
special inspection with 
MASTER-Amur, MASTER-Tunka, MASTER-Kislovodsk, MASTER-OAFA and MASTER-SAAO 
telescopes.  We cover 50.2% initial probability now up to 20.5 mag.


The first OT  MASTER OT J090021.21+635049.7 detection ( Possible SN in 
1.797"  from Sloan galaxy).


MASTER-Kislovodsk auto-detection system discovered OT source at (RA, Dec) 
= 09h 00m 21.21s +63d 50m 49.7s on 2017-01-05.06666 UT.
The OT unfiltered magnitude is 18.6m+-0.2 (limit 19.9m).

The OT is seen in 4 image.

We have reference image without OT on 2012-10-20.91652 UT with unfiltered 
magnitude limit 19.7m.

No known minor planets, brighter than V = 21.0, were found in the 
15.0-arcminute region around R.A. = 09 00 21.21, Decl. = +63 50 49.7 
(J2000.0) on 2017 01 05.07 UT .

OT is offset  1.79709" from the Sloan galaxy rmag=19.96, gmag=20.64 
http://skyserver.sdss.org/dr9/en/tools/chart/navi.asp?ra=135.08928453&dec=63.84745156

Spectral and photometrical observations are required .

The discovery and reference images are available at:

http://master.sai.msu.ru/static/OT/090021.21635049.7.png