TITLE: GCN CIRCULAR NUMBER: 10576 SUBJECT: INTEGRAL Alert n. 5995: MASTER-Net optical observations DATE: 10/04/04 15:26:04 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs D.Kuvshinov, E. Gorbovskoy, V. Lipunov, V.Kornilov, A.Belinski, N.Shatskiy, N.Tyurina, P.Balanutsa, V.V.Chazov, P.V.Kortunov, A.Kuznetsov, D.Zemnukhov, M. Kornilov Sternberg Astronomical Institute, Moscow State University V.Yurkov, Yu.Sergienko, D.Varda, A.Garusina Blagoveschensk Educational State University, Blagoveschensk A. Tlatov, A.V. Parhomenko, D. Dormidontov Kislovodsk Solar Station of the Pulkovo Observatory V.Krushinski, I.Zalozhnih, T.Kopytova, A. Popov Ural State University, Kourovka K.Ivanov, S.Yazev, N.M.Budnev, E.Konstantinov, V.Lenok Irkutsk State University Two MASTER robotic telescopes (MASTER-Net: http://observ.pereplet.ru) located at Vostryakovo (Moscow) and Tunka-Baykal was responted to the GRB 100403A (Integral alert 5995) 16 sec after Notice time and 35 s after the GRB time and 36 sec after Notice time and 55 s after the GRB time. Baykal weather is bad. Moscow weather is good. The Moscow result is: T-T_grb Exp m_lim Band 36 30s 17 Unfiltered The optical star HDE 245770 (~9m V) not saturated (companion of the X-ray pulsar A0535+26). It is interesting that both last INTEGRAL and Swift BAT alerts (GCN 10561, GCN 10573) are the result activity of the X-ray Pulsars with Be stars ( A0535+26 and LS V +44 17). By the way the X-ray pulasar A0535+26 is the NS with high magnetic field ~ 10^14 Gs (see very old paper Lipunov 1982, Soviet Astronomy, vol. 26, 537 or monograph: V.M. Lipunov, "Astrophysics of Neutron Stars", Springer-Verlag, Berlin, New-York, 1992). The message may be cited. mailto: lipunov@sai.msu.ru