[Previous] | [Session 39] | [Next]

[39.04] Quasi-Periodic Oscillations and Outflows Driven by Magnetic Interaction between a Neutron Star and its Surrounding Disk

Y. Kato (Chiba University), M.R. Hayashi (NAOJ), R. Matsumoto (Chiba University), S. Miyaji (Chiba University)

We carried out 2.5 dimensional numerical simulations of the interaction between a weakly magnetized neutron star and its accretion disk in Low Mass X-ray Binaries (LMXBs). General relativistic effects are incorporated by using Pseudo-Newtonian potential.

At the initial state, we assume that a disk truncated at r=r_in rotates in the dipole magnetic field of the neutron star. The magnetic loops, which connect the neutron star and the disk, expand as the magnetic twist is injected from the disk to the loops. Magnetic reconnection taking place in the current sheets formed in the loops triggers X-ray flares and hot plasma ejection (Hayashi et al. 1996).

Our numerical results show that the magnetic reconnection and the plasma outflows take place intermittently close to a neutron star in LMXBs. Frequency analysis reveals that the central frequency of the time variation of mass accretion rate is \approx 1 kHz assuming that the mass of the neutron star is 1.4 M_\odot. The frequency depends on the strength of initial magnetic field threading the disk.

We study the dependence of numerical results on rotation angular velocity of the neutron star, plasma \beta of the accretion disk, and accretion rate (\dot{M}). Aperiodic X-ray flares and outflows of hot plasma inevitably accompany kHz QPOs in LMXBs.