TITLE:   GCN CIRCULAR
NUMBER:  13922
SUBJECT: GRB 121027A: MASTER early prompt optical limit
DATE:    12/10/29 11:09:57 GMT
FROM:    Vladimir Lipunov at Moscow State U/Krylov Obs  <gcncirc@observ.inetcomm.ru>

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

C. Mallamaci, C. Lopez and F. Podest
Observatorio Astronomico Felix Aguilar (OAFA)

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

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

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

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

V. Krushinski, I. Zalozhnich,  A. Popov, A. Bourdanov
Ural Federal University


MASTER-ICATE robotic Very Wide Field Cameras (FOV=2x384 square degrees,
D=72mm, f/1.2, 1 pix = 22 arcsec, http://observ.pereplet.ru) located in
Argentina (Observatorio Astronomico Felix Aguilar,
http://93.180.27.230:8080/) were pointed to the GRB 121027A by Swift 
trigger (Evans et al., GCNC 13906)   85 s after GRB time at 
2012-10-27 07:33:54 UT.
We haven`t found  optical transient  within Swift XRT 
error-box  on our first (1 s exposure) set and on coadd image
with complete exposure
of 11 seconds during gamma-burst activity (Barthelmy et al., GCN 13910).

The 5-sigma upper limit on unfiltered (with respect to Tyho V mag) single 
image has  been about 11.0 mag and 11.7 mag on coadded image.

The automatic photometry is:

Date         time     Exp.time	Limit
                        Coadd

2012-10-27 07:33:54     11      11.7
2012-10-27 07:35:05     41      12.2
2012-10-27 07:37:25     7       11.2
2012-10-27 07:38:16     80      11.7
2012-10-27 07:44:18     17      11.2
2012-10-27 07:45:18     75      12.2
2012-10-27 07:50:38     11      11.6
2012-10-27 07:51:03     26      12.1
2012-10-27 07:51:56     30      12.2


Our cameras are continuously imaging the sky with 1 sec exposures without 
time gap.

This message can be cited.