TITLE: GCN CIRCULAR NUMBER: 24395 SUBJECT: IceCube-190504A: MASTER optical follow-up observations DATE: 19/05/05 08:23:03 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, N.Tyurina, V.Kornilov, D.Vlasenko, V.Vladimirov, D.Zimnukhov, A.Kuznetsov, P.Balanutsa, A. Chasovnikov, V.Topolev, F.Balakin, K.Zhirkov, D.Kuvshinov (Lomonosov Moscow State University, SAI, Physics Department), R. Podesta, C. Lopez, C.Francile, F. Podesta (Observatorio Astronomico Felix Aguilar OAFA, San Juan National University), H.Levato (Instituto de Ciencias Astronomicas, de la Tierra y del Espacio ICATE, SJNU) R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres (The Instituto de Astrofisica de Canarias), D. Buckley (South African Astronomical Observatory), O. Gress, N.M. Budnev, O.Ershova, S.Yazev (Applied Physics Institute, Irkutsk State University), V. Yurkov, A. Gabovich, Yu. Sergienko, D. Kobcev (Blagoveschensk Educational State University), A. Tlatov, V.Senik, A.V. Parhomenko, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the IceCube Alert190504.77 39 sec after notice time and 133 sec after trigger time at 2019-05-04 18:27:31 UT. MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina ( Observatorio Astronomico Felix Aguilar ) was pointed to the IceCube Alert190504.77 at 2019-05-04 23:10:52.949 UT. The cover map and images limits are available at https://master.sai.msu.ru/site/master2/event.php??not=2019-05-04%2018:26:52&sat=IceCube&gcrd=(65.7833d,-37.4425d)&eb=1.23&trig=2019-05-04%2018:25:18&n=Alert190504.77 The message may be cited.