GCN Circular 16307

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

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

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-Net: http://observ.pereplet.ru) 
located in  Tunka  began observations of   GRB140512A  (Pagani et. al. GCN 
16249
Not found
 
 
) from  pointing  on several FERMI alerts.
During the second set of observations by FERMI coordinates the GRB140512A 
error box was covered by our  very wide field cameras MASTER VWF 
(FOV=2x384 square degrees, D=72mm, f/1.2, 1 pix = 22 arcsec) which 
installed on  MASTER-II telescope. So we have 5 images with 5 second 
exptime without time gap since 2014-05-12 19:32:38 i.e. 29 sec. after the 
trigger and 49 sec. after the burst. We did not see optical transient 
(Pagani et. al. GCN 16249
Not found
 
 
)  at GRB140512A place. The  5-sigma upper limit 
on coadd of 5 MASTER-VWF images since 49 sec. till 74 sec. after the burst 
has been about 12.3 mag. The prompt images available here 
http://master.sai.msu.ru/static/GRB/GRB140512A.png .

After several repointing by FERMI alerts MASTER II was pointed to the 
GRB140512A 171 sec after trigger time at 2014-05-12 19:34:40.212 UT in two 
polarizations by Swift coordinates. We definitely see OT on our images in 
both polarizations.

Out final light curve  is  available in Tab. 1

        Start time       Exptime T-T_mid     P/      eP/      P\    eP\
2014-05-12T19:34:40.212     30     186    14,45    0,04    14,37  0,03
2014-05-12T19:36:37.643     60     318    14,72    0,05    14,74  0,04
2014-05-12T19:38:24.484     60     425    15,60    0,12    15,35  0,06
2014-05-12T19:39:47.447     60     508    15,41    0,10    15,65  0,07
2014-05-12T19:41:10.651     60     591    15,75    0,13    15,75  0,08
2014-05-12T19:42:32.663     60     673    15,98    0,16    15,94  0,09
2014-05-12T19:43:54.083     60     754    16,46    0,22    16,42  0,12
2014-05-12T19:45:56.002    170     931    16,37    0,20    16,79  0,15
2014-05-12T19:50:30.564    180    1211    17,50    0,39    16,84  0,15
2014-05-12T19:56:11.667    180    1552    16,82    0,27    17,57  0,22

P/ and P\ is a polarization filter which are oriented at an angle 45 and 
135 degrees to RA axis respectivel.  eP/ and eP\ is a error of P/ and P\ 
values.  T is a  GRB trigger time.

The dimensionless Stokes parameter averaged over 5 first expositions is 
estimated to be less than observational error which equals to 2.9% (i.e. q 
= 0.3 +- 2.9%). So big error is connected to observation in a morning 
twilight (sun altitude ~ 12 d) and high object zenith distance (z ~ 70 d).

Our  unfiltered magnitude is well described by a parity 0.8R + 0.2B  (USNO-B1)

The message may be cited.