AAS 199th meeting, Washington, DC, January 2002
Session 95. Accreting Neutron Stars
Display, Wednesday, January 9, 2002, 9:20am-6:30pm, Exhibit Hall

## [95.12] Global MHD Simulations of the Accretion Flow Plunging into the Magnetosphere between a Neutron Star and its Accretion Disk

Y. Kato (Chiba University), M.R. Hayashi (National Astronomical Observatory of Japan), S. Miyaji, R. Matsumoto (Chiba University)

We carried out two dimensional magnetohydrodynamic (MHD) simulations of the accretion flow around a weakly magnetized neutron star including the transition layer between the magnetosphere and its accretion disk. General relativistic effects are taken into account by using the pseudo-Newtonian potential. At the initial state we assume a rotating torus threaded by the dipole magnetic field of the neutron star. The inner edge of the torus locates 30 Schwartzschild radius (rg). The torus matter accretes by losing angular momentum magnetically. Our simulation results show that aperiodic disk oscillations whose frequency is about the epicyclic frequency \kappa2=2\Omega(2\Omega+r{d\Omega\over d r}) where \Omega is the angular rotation speed at disk-magnetosphere boundary generate quasi-periodic oscillations of accretion flow toward the magnetic poles of the neutron star. The typical oscillation frequency is 100 - 2000 Hz. When 107 G\leq Bsurface<109 G, we found that magnetic reconnection takes place intermittently in magnetic loops connecting the neutron star and its accretion disk. As a consequence, hot plasmas generated by the magnetic reconnections produce hard X-ray emission from the region r = 5 - 10 rg and plasmoids are ejected by magnetic reconnection. Such QPO sources inevitably accompany X-ray flares and bipolar outflows of hot X-ray emitting plasma. Futhermore, high energy electrons produced by magnetic reconnection can be the origin of Radio emission observed in Z-sources.