TITLE: GCN CIRCULAR NUMBER: 18613 SUBJECT: GRB GRB 151118A: MASTER-NET optical observations DATE: 15/11/18 11:11:38 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E.Gorbovskoy, N.Tyurina, V.Kornilov, P.Balanutsa, A.Kuznetsov, D. Vlasenko, D.Kuvshinov Lomonosov Moscow State University, Sternberg Astronomical Institute R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres The Instituto de Astrofisica de Canarias A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Senik Kislovodsk Solar Station of the Pulkovo Observatory MASTER II robotic telescope (MASTER-Net: http://observ.pereplet.ru) located in Kislovodsk was pointed to the GRB151118.13 30 sec after notice time and 44 sec after trigger time at 2015-11-18 03:07:17 UT. On our first (10s exposure) set we haven`t found optical transient within SWIFT error-box (ra=03 48 37 dec=+65 52 06 r=0.05). The 5-sigma upper limit has been about 16.5 mag unfiltered. MASTER II robotic telescope (MASTER-Net: http://observ.pereplet.ru) located in IAC was pointed to the GRB151118A 24 sec after notice time and 42 sec after trigger time at 2015-11-18 03:07:12 UT in two polarizations. On our first (10s exposure) set we haven`t found optical transient within SWIFT error-box (Amaral-Rogers et al GCN 18611). Our early upper limits on single and coadd images given in a table below: Table 1. 5 sigma limit. T-Ts T-Tm Expt. P| P- coadd. lim lim ---------------------------------------- 42 47 10 16.7 16.8 1 42 90 50 17.9 18.0 3 42 508 790 19.9 20.0 12 86 96 20 17.3 17.4 1 117 127 20 17.3 17.4 1 147 218 120 18.7 18.8 3 299 420 220 19.2 19.3 3 551 762 400 19.6 19.7 3 --------------------------------------- T - is a trigger time [s]. Ts - image start time [s]. Tm - image middle time [s]. Expt - exposure time [s]. P| - image upper limit in polarizer orientated 90 deg. to RA axis [mag]. P- - image upper limit in polarizer orientated 0 deg. to RA axis [mag]. We do not see OT brighter 20 mag. There is marginal object (m~20) with 6" W (RA) and 3"S (dec) offset from XRT error box center (Ra = 03h 48m 40.40s Dec= 65d 54m 01.3s Mag ~ 20.3 +- 0.7 ). The message may be cited.