TITLE: GCN CIRCULAR NUMBER: 18576 SUBJECT: GRB 151107B: MASTER-NET OT detection inside the FERMI error box DATE: 15/11/10 21:15:27 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres The Instituto de Astrofisica de Canarias E. Gorbovskoy, V. Lipunov, V.Shumkov, N.Tyurina, V.Kornilov, P.Balanutsa, A.Kuznetsov, D. Vlasenko Lomonosov Moscow State University, Sternberg Astronomical Institute D.Buckley, S. Potter, A.Kniazev, M.Kotze South African Astronomical Observatory A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Senik Kislovodsk Solar Station of the Pulkovo Observatory O.Gress, K.Ivanov, N.M.Budnev, V.A.Poleshchuk Irkutsk State University V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov Blagoveschensk Educational State University, Blagoveschensk V.Krushinski, I.Zalozhnih Ural Federal University, 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 IAC (Tenerife, Spain) was pointed to the FERMI GBM GRB151107B 14 sec after notice time and 60 sec after trigger time at 2015-11-07 20:25:52 UT. Our first (10s exposure) set limit is 16.8 within FERMI error-box (ra=00 42 28 dec=+48 48 58 r=4.5, Stanbro and Meegan, GCN 18570). MASTER II robotic telescope located in Kislovodsk was pointed to the GRB151107B 21 sec after notice time and 66 sec after trigger time at 2015-11-07 20:25:59 UT. Our first (10s exposure) set limit is 18.1 within FERMI error-box . The summary (60sec) unfiltered optical limit is 19.5m. MASTER II robotic telescope located in SAAO (South Africa, Sutherland) was pointed to the GRB151107B 20 sec after notice time and 66 sec after trigger time at 2015-11-07 20:25:58 UT. Our first (10s exposure) set limit is 15.4. There are prompt pointing observations because duration of the GRB is ~140 s (Stanbro and Meegan, GCN 18570) After 5 minutes of alert observations of the center of error box, telescopes in IAC and Kislovodsk started the inspect survey inside large Fermi error box (ra=00 42 28 dec=+48 48 58 r=4.533300) obtained by GCN socket. As a result, we cover more than 98% of 1 sigma+systematic and 85% of 3-sigma + systematic of the FERMI GBM final error box (Stanbro et. al. GCN 18570) with upper limit up to 19 mag during this night. The coverage map is available here: http://master.sai.msu.ru/static/GRB/GRB151107B.png There is 1 possible OTs was found up to now - MASTER OT J015539.85+485955.6 published yesterday (Shumkov et al., Atel #8262). (RA, Dec) = 01h 55m 39.85s +48d 59m 55.6s The OT mag is 15.2 on 2015-11-07.99775 UT. The specrtrum was done by follow up Liverpool Telescope (La Palma) observations shows a broad continuum, consistent with that expected from a dwarf nova in outburst ( Piascik & Steele, ATel #8265). The brightness is not sufficiantly changed after half of the day (during independently ASAS detection Holoin et al., ATEL #8260) and our today imaging (2015-11-10 17:16:26.513UT, m_OT=15.5+-0.1) shows that OT doesn't fade essntially with respect to discovery magnitude contraverse to GRB optical afterglow . The search is continuing. The message may be cited.