TITLE: GCN CIRCULAR NUMBER: 16307 SUBJECT: GRB 140512A: MASTER prompt and afterglow optical observations DATE: 14/05/19 05:47:51 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs 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) 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) 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.