TITLE: GCN CIRCULAR NUMBER: 22593 SUBJECT: GRB 180404A: MASTER-OAFA OT observation DATE: 18/04/04 05:30:33 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, A.Kuznetsov, V.Chazov, I. Gorbunov, D. Vlasenko, D.Kuvshinov, P.Balanutsa Lomonosov Moscow State University, Sternberg Astronomical Institute, Moscow State University R. Podesta, Carlos Lopez and F. Podesta Observatorio Astronomico Felix Aguilar (OAFA) Hugo Levato and Carlos Saffe Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE) A. Tlatov, V.Senik, D. Dormidontov Kislovodsk Solar Station of the Pulkovo Observatory V. Yurkov, A. Gabovich, Yu. Sergienko Blagoveschensk Educational State University, Blagoveschensk O. Gres, N.M. Budnev, O. Chuvalaev, Yu.Ishmuhametova Irkutsk State University R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres The Instituto de Astrofisica de Canarias D. Buckley, S. Potter South African Astronomical Observatory MASTER-OAFA robotic telescope (MASTER-Net: http://observ.pereplet.ru) located in Argentina was pointed to the GRB180404A (Gropp et al. GCN 22589) 21 sec after notice time and 43 sec after trigger time at 2018-04-04 00:46:18 UT. On our first 10s exposure set we haven`t found optical transient with 17.4 5-sigma upper limit in SWIFT XRT error-box (ra=83.549 dec=-37.17 r=4.2"). MASTER auto-detection system detected OT with RA,Dec=5h 34m 11s.66, -37d 10m 03s.5 with unfiltered m_OT=19.8 on the summary image with 660s exposition started 2018-04-04 00:46:18.938UT, that was discovered by Swift (Gropp et al. GCN 22589) and confirmed by VLT (Selsing et al. GCN 22591) ==================================================================== The observations made on zenit distance = 42 degrees, galaxy latitude b = -30 degree. The moon (87 % bright part) below the horizon (The altitude of the Moon is -1 degree ). The sun altitude is -29.7 degree. The message may be cited. 1