TITLE: GCN CIRCULAR NUMBER: 10231 SUBJECT: GRB 091020: MASTER-Net optical polarization observations DATE: 09/12/02 19:15:38 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.Zemnukhov, M. Kornilov Sternberg Astronomical Institute, Moscow State University V.Krushinski, I.Zalozhnih, T.Kopytova Ural State University, Kourovka A. Tlatov, A.V. Parhomenko, D. Dormidontov Kislovodsk Solar Station of the Pulkovo Observatory K.Ivanov, S.Yazev, N.M.Budnev, E.Konstantinov, V.Lenok Irkutsk State University S.Sergienko, V.Yurkov Blagoveschensk Educational State University, Blagoveschensk MASTER II robotic telescope (MASTER-Net: http://observ.pereplet.ru, 2x400 mm, 2x 4 square degrees, 2x16Mpx Apogee CCD) located at Kislovodsk was pointed to the GRB 091020 (Racusin et al., GCN 10048) by internet 3422 s after the GRB time. The large delay was caused with technical problems on site (Gorbovskoy et al., GCN 10052). The first 7 images was taken in R-band. The exposure each images is 180s. West-telescope GRB Time OT Mag Error 1.02097639 17.93 0.22 1.07643278 17.43 0.09 1.13188834 17.78 0.14 1.18734417 18.03 0.19 1.24280056 17.87 0.15 1.29825584 17.58 0.10 1.35371584 17.94 0.12 The result of the unfiltred polarization combined images is: West-telescope GRB Time OT Mag Error (Hours) 1.604558 18.65 0.10 1.983004 18.91 0.08 2.285582 19.04 0.08 2.562864 19.28 0.11 2.84015 19.36 0.09 3.117435 19.32 0.08 3.394721 19.35 0.06 3.672004 19.23 0.10 3.949285 20.07 0.16 4.226602 20.67 0.28 4.503883 20.07 0.22 East-telescope GRB Time GRB Error (Hours) 1.604718 18.60 0.06 1.983232 18.46 0.06 2.285826 19.14 0.09 2.563109 19.11 0.09 2.84039 19.56 0.10 3.117671 19.38 0.09 3.394954 19.70 0.17 3.672234 19.53 0.11 3.949516 19.92 0.16 4.226796 20.03 0.19 4.50408 19.99 0.16 Using all our polarizated magnitudes we find that the light curve is very well described by a single power-law decay with alpha = 1.2 +/- 0.1, that is in good agreement with the following observations (Kann et al., GCN 10076) The light curve of our observations is available at http://observ.pereplet.ru/images/GRB091020/grb.html . The message may be cited. mailto: lipunov@sai.msu.ru