TITLE: GCN CIRCULAR NUMBER: 16806 SUBJECT: GRB 140907A: MASTER optical observations DATE: 14/09/09 13:03:53 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs E. Gorbovskoy, V. Lipunov, M.Pruzhinskaya, V.Kornilov, D.Kuvshinov, N.Tyurina, N.Shatskiy, P.Balanutsa, D.Zimnukhov, A.Kuznetsov, V.V.Chazov, D.Denisenko, A.Sankovich Lomonosov Moscow State University, Sternberg Astronomical Institute, Moscow State University V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov, A. Gabovich Blagoveschensk Educational State University, Blagoveschensk K.Ivanov, S.Yazev, N.M.Budnev, O.Gres, O.Chuvalaev, V.A.Poleshchuk Irkutsk State University V.Krushinski, I.Zalozhnih, A. Popov Ural Federal University, Kourovka A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Sennik Kislovodsk Solar Station of the Pulkovo Observatory 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 Blagoveschensk was pointed to the GRB140907A 6987 sec after notice time and 7504 sec after trigger time at 2014-09-07 18:12:13 UT directly after weather conditions became suitable. On our first (180s exposure) set we found optical transient within Swift error-box (ra=03 12 34 dec=+46 36 18 r=0.050000) on coadditional images in two epoch. The protometry results available at Table 1. Table 1. Date and Time start T_trig-Tmid Exptime Mag err.mag 2014-09-07 18:12:13.4 7809 540 19.0 0.2 2014-09-07 19:23:43.6 12547 1260 19.4 0.2 The approximate power law index (alpha) from 7000 to 13000 seconds after the trigger is about 0.81 +- 0.1 (F ~ t^-alpha). Another two MASTER-II robotic telescop located in Kislovodsk and Tunka made upper limit observations only in earlier time due to weather conditions and high zenith distance of object. MASTER II in Tunka was pointed to the GRB140907A 1021 sec after trigger time at 2014-09-07 16:24:10 directly after weather conditions became suitable. On our first (180s exposure) image we haven`t found optical transient up to 16m. MASTER II in Kislovodsk starting observations GRB140907A 17 sec after notice time and 77 sec after trigger time at 2014-09-07 16:08:25 using FERMI GBM coordinates. However OT position was not covered by MASTER-II. The telescope pointing by Swift trigger 22 sec after notice time and 540 after trigger time at 2014-09-07 16:16:08. On first (110s exposure) image we haven`t found optical transient up to 12.5 m. The zenith distance of object z~85 d. Our white (clear) band is well described by a parity 0.8R+0.2B (USNO B1).