TITLE: GCN CIRCULAR NUMBER: 13635 SUBJECT: GRB 120811C: MASTER-Tunka OT observations DATE: 12/08/13 07:05:34 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs K.Ivanov, S.Yazev, N.M.Budnev, O.Gres, O.Chuvalaev, V.A.Poleshchuk Irkutsk State University E. Gorbovskoy, V. Lipunov, V.Kornilov, D.Kuvshinov, A.Belinski, N.Tyurina, N.Shatskiy, P.Balanutsa, D.Zimnukhov, A.Kuznetsov, V.V.Chazov, A.Kuznetsov, A.Sankovich Sternberg Astronomical Institute, Moscow State University V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov Blagoveschensk Educational State University, Blagoveschensk A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Sennik Kislovodsk Solar Station of the Pulkovo Observatory 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 was pointed to the GRB120811C (Barlow et al., GCN 13622) 40 sec s after notice time and 676 sec after GRB time at 2012-08-11 15:46:08.449 UT. On our first (130s exposure) set we have found OT within SWIFT-BAT error-box in two polarizations. The preliminary robotic photometry (m=0.2B + 0.8R, Usno B magnitudes) is: datetime coord2000 Band mag error 2012-08-11 15:46:08.449 13h 18m 43.90s , +62d 18m 02s.1 P| 17.3 0.2 2012-08-11 15:46:09.684 13h 18m 43.86s , +62d 18m 02s.3 P- 17.2 0.1 2012-08-11 15:49:12.268 13h 18m 43.76s , +62d 18m 02s.3 P| 17.6 0.2 2012-08-11 15:49:12.282 13h 18m 43.93s , +62d 18m 02s.6 P- 17.6 0.2 2012-08-11 15:52:52.452 13h 18m 43.75s , +62d 18m 01s.8 P| 17.8 0.2 So, MASTER-Net have simultaneous optical observations in four polarizations (see Denisenko et al., GCN 13623) of GRB120811C. The message may be cited.