TITLE: GCN CIRCULAR NUMBER: 23245 SUBJECT: GRB 180914B: MASTER OT automatic dtection DATE: 18/09/17 11:10:54 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, N.Tiurina, D. Vlasenko, V.Kornilov, A.Kuznetsov, V.Chazov, I. Gorbunov, D.Zimnukhov, D.Kuvshinov, P.Balanutsa, V.Vladimirov, Lomonosov Moscow State University,SAI D.Svinkin (Ioffe Institute, Sankt Petersburg) A. Tlatov, V.Senik, D. Dormidontov Kislovodsk Solar Station of the Pulkovo Observatory D. Buckley, South African Astronomical Observatory (SAAO) R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres The Instituto de Astrofisica de Canarias (IAC) R. Podesta, F. Podesta, C. Lopez, C.Francile Observatorio Astronomico Felix Aguilar (OAFA) H.Levato, Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE) O. Gres, N.M.Budnev , Yu.Ishmuhametova Irkutsk State University (ISU) A. Gabovich, V. Yurkov, Yu. Sergienko Blagoveschensk Educational State University (BSPU) MASTER-Tunka robotic telescope (MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Tunka Astrophysical Center (Baykal Lake, Applied Physics Institute, Irkutsk State University, Russia) was starting survey on the LAT GRB180914.77 error-box (ra=22 09 47 dec=+24 52 47 r=0.33) 9409 sec after notice time and 79012 sec after trigger time at 2018-09-15 16:19:55 UT. The 5-sigma upper limit on our first (180s exposure) set is about 19.7 mag MASTER OT J220925.53+250343.3 - Afterglow MASTER-Tunka auto-detection system discovered OT source at (RA, Dec) = 22h 09m 25.53s +25d 03m 43.3s on 2018-09-15 16:19:55.393UT. Error is 0.7 arcsec. This position is coincident with late XRT (P. A. Evans, GCN 23234) and KAIT (WeiKang Zheng and Alexei V. Filippenko, GCN 23237) positions. The OT magnitude in clear filter is 19.2m (limit 19.7m). This is the first optical magnitude ( see also Eleonora Troja GCN 23238, A. de Ugarte Postigo et al., GCN 23239; N. Paul M. Kuin et al., GCN 23241; Eleonora Troja et al., GCN 23243). The OT is seen in 2 images. There is no minor planet at this place. We have reference image without OT on 2011-12-15.46200 UT with unfiltered magnitude limit 20.0m. The discovery and refernces images are available at http://master.sai.msu.ru/static/OT/MASTEROTJ220925.53+250343.3.jpg The galactic latitude b = -25 deg. The observations made on zenit distance = 28 deg.The moon (38 % bright part) below the horizon (The altitude of the Moon is -17 deg. ). The sun altitude is -34.5 deg. The object can be observed till sunrise at 2018-09-15 22:42:06