TITLE: GCN CIRCULAR NUMBER: 11231 SUBJECT: GRB 100906A: MASTER preliminary polarization prompt light curve DATE: 10/09/06 15:23:17 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs E. Gorbovskoy, V. Lipunov, V.Kornilov, A.Belinski, N.Shatskiy, N.Tyurina, D.Kuvshinov, P.Balanutsa, V.V.Chazov, P.V.Kortunov, A.Kuznetsov, D.Zimnukhov, M. Kornilov Sternberg Astronomical Institute, Moscow State University K.Ivanov, O.Chuvalaev, V.Poleschuk, E.Konstantinov, V.Lenok, O.Gres, S.Yazev, N.M.Budnev, Irkutsk State University V.Yurkov, Yu.Sergienko, D.Varda, I.Kudelina Blagoveschensk Educational State University, Blagoveschensk V.Krushinski, I.Zalozhnich, T.Kopytova, A. Popov Ural State University, Kourovka A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Sennik Kislovodsk Solar Station of the Pulkovo Observatory Two MASTER robotic telescopes (MASTER-Net: http://observ.pereplet.ru) located near Baykal Lake (Tunka) and Blagoveschensk was pointed to the Swift GRB 100906A (Markwardt et al., GCN CIRCULAR 11227) 23 sec after Notice time (38 s after trigger time) and 43 s after Notice time (58s after trigger time) (Ivanov et al., GCN CIRCULAR 11228). We see brightening and decay of the prompt optical emission in both polarizations. The preliminary light curve is available at http://observ.pereplet.ru/images/GRB100906A/pre_lc.gif This automatical phtometry calbrated by USNOB1 stars. The message may be cited. mailto: lipunov@sai.msu.ru