1. 1-3 November 20062 nd EAST-ASIA NUMERICAL ASTROPHYSICS MEETING (KASI, Daejeon, Korea) Numerical Simulations of Relativistic Expansion of Magnetic Arcades in Magnetars Eiji Asano 1, Hiroyuki Takahashi 1 and Ryoji Matsumoto 2 1:Graduate School of Science and Technology, Chiba University 2:Department of Physics, Faculty of Science, Chiba University

2. Soft  -ray Repeaters According to a model of soft  -ray repeaters proposed by Thompson & Duncan (2001), we simulated the relativistic expansion of magnetic arcades. To study the mechanism of the releasing energy in magnetars, we carried out simulations of two models relativistic force-free equations. The codes are based on HLL method. (NASA Marshall Spaceflight Center)

3. Simulations Local simulation (2.5D Relativistic MHD eqs.) Model A: Interaction of neutron star and its disk (Asano et al., 2005) This model can be applied the disk is formed around the magnetar. Result: Magnetic loops connecting neutron star and its disk is twisted, they expand relativistic speed. Result: The plasma velocity reaches the speed of light in the case of a strongly magnetic field.

4. Simulations Model B: Isolated neutron star A tangled magnetic field inside a magnetar creates rising magnetic arcades. Result: When critical twist is accumulated in the arcades, the relativistic expansion of magnetic arcades occur. (Lorents factor  >10)