TITLE: GCN CIRCULAR NUMBER: 20732 SUBJECT: LIGO/Virgo G274296: MASTER new OT DATE: 17/02/24 13:21:31 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V.M. Lipunov, V.Shumkov, E. Gorbovskoy, N.Tyurina, P.Balanutsa, V.G. O.Gress, Kornilov, A.Kuznetsov, M.I.Panchenko, A.V.Krylov, I.Gorbunov Lomonosov Moscow State University, Sternberg Astronomical Institute N.M. Budnev, O. Gress, K. Ivanov, S.Yazev Irkutsk State University R.Podesta, C.Lopez, F. Podesta Observatorio Astronomico Felix Aguilar (OAFA) , National University of San Juan, Argentina H. Levato, C. Saffe Instituto de Ciencias Astronomicas,de la Tierra y del Espacio (ICATE), San Juan, Argentina D.Buckley, S. Potter, M. Kotze, South African Astronomical Observatory R. Rebolo, M. Serra-Ricart, G. Israelian, N.Lodiu The Instituto de Astrofisica de Canarias A. Tlatov, V.Sennik Kislovodsk Solar Station of the Pulkovo Observatory V.Yurkov, Yu.Sergienko, A.Gabovich Blagoveschensk Educational State University, Blagoveschensk MASTER continues inspection of LIGO event G274296 (Shawhan et al. GCN 20689, Lipunov et al. GCN 20696, GCN 20715; 20712; ). The cover map of MASTER inspection survey, the position of MASTER OTs inside LIGO error-box is presented at http://master.sai.msu.ru/static/MASTERGW170217full.jpg MASTER OT J184722.28-834543.4 discovery - new optical transients, no known sources in VIZIER database. MASTER-OAFA auto-detection system discovered OT source at (RA, Dec) = 18h 47m 22.28s -83d 45m 43.4s on 2017-02-24.13990 UT with unfiltered m_OT=17.6m (mlimit=19.4m). The OT is seen in 2 images. There is no minor planet at this place. We have reference images without OT on 2017-01-26.20851 UT with 19.7m unfiltered magnitude limit in MASTER-OAFA, on 2016-08-05 18:16:52UT with mlim=19.5, on 2016-03-02 23:53:05 with mlim=20.0, 2015-04-26 23:34:52 with mlim=20.0, on2015-01-12 01:41:57UT with mlim=19.6 in MASTER-SAAO database. There is no any known sources inside 8" in VIZIER database, it means 22mag of POSS historical limits and more then 4.4magnitude of current outburst amplitude. Spectral observations are required. The discovery and reference images are available at: http://master.sai.msu.ru/static/OT/184722.28-834543.4.png