TITLE: GCN CIRCULAR NUMBER: 15553 SUBJECT: GRB 131125A: MASTER-Net very early optical observations DATE: 13/11/29 18:47:14 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs Gorbovskoy, V. Lipunov,D.Denisenko, V.Kornilov, D.Kuvshinov, N.Tyurina, N.Shatskiy, P.Balanutsa, D.Zimnukhov, A.Kuznetsov, V.V.Chazov, Sternberg Astronomical Institute, Moscow State University K.Ivanov, S.Yazev, N.M.Budnev, O.Gres, O.Chuvalaev, V.A.Poleshchuk Irkutsk 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.Krushinsky, I.Zalozhnih, A. Popov Ural Federal University, Yekaterinburg, 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 Kislovodsk was pointed to the GRB131125A 10 s after notice time and 24 sec after GRB time at 2013-11-25 16:33:25 UT. But IPN error box (GCN 15546) was outside of FOV of our MASTER-II telescope and very wide field camera (usually we follow up all Fermi alerts). After first coordinates specification we cover IPN error box using very wide field cameras. The first images covered error-box was obtained 49 sec after GRB time at 2013-11-25 16:33:40 UT. The 5-sigma upper limit has been about 12 mag on single 5 seconds exposure images and 13.5 on coadd of first 14 consecutive images The 5-sigma upper limit has been about 14.1 mag We find several optical marginal candidates to OT. Name R.A. Dec. m MASTER_1 114.775649 46.120371 13.6 MASTER_2 114.597740 48.927898 13.7 MASTER_3 114.835195 47.047021 13.0 One sigma coordinate error is +- 7 arcsec. The first image available here: http://master.sai.msu.ru/static/GRB/GRB131125_first.jpeg The coadd images here: http://master.sai.msu.ru/static/GRB/GRB131125_coadd.jpeg The message may be cited.