TITLE: GCN CIRCULAR NUMBER: 10203 SUBJECT: GRB 091127: MASTER early optical transient polarimetry DATE: 09/11/28 16:31:40 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs A.Belinski, E. Gorbovskoy, V. Lipunov, V.Kornilov, D.Kuvshinov, N.Shatskiy, N.Tyurina, P.Balanutsa, V.V.Chazov, D. Zemnukhov, A.Kuznetsov Sternberg Astronomical Institute, Moscow State University A. Tlatov, A.V. Parkhomenko, D. Dormidontov Kislovodsk Solar Station of the Pulkovo Observatory V.Krushinski, I.Zalognikh, T.Kopytova, A. Popov Ural State University, Kourovka S.Yazev, K.Ivanov, N.M.Budnev, E.Konstantinov, V.Lenok Irkutsk State University V.Yurkov Blagoveschensk Educational State University, Blagoveschensk MASTER II robotic telescope (MASTER-Net: http://observ.pereplet.ru, D= 2x400 mm, FOV= 2x4 square degrees, 2x16 Mpx Apogee CCD) located at Kislovodsk (2000m) was responted to the GRB 091027 (Troja et al., GCN 10191) 9 sec after Notice time and 91 s after the GRB time at very large zenit distance (~4 degrees up to horizont). We saw bright optical counterpart (~14 mag, 91-111 sec after GRB Time) at Liverpool position (Smith et al., GCN 10192) in both polarizations. We took ~20 images with synchronous exposition in two polarizations before GRB setting with growing exposition from 20 to 160 sec. We saw possible brightening around 2 min (after GRB Time). The reduction is continued. The message may be cited. mailto: lipunov@sai.msu.ru