Evolution of the Relativistic Plasmoid-Chain in the Poynting-Dominated Plasma

In this paper, we investigate the evolution of the plasmoid-chain in a Poynting-dominated plasma. We model the relativistic current sheet with cold background plasma using the relativistic resistive magnetohydrodynamic approximation, and solve its temporal evolution numerically. We perform various calculations using different magnetization parameters of the background plasma and different Lundquist numbers. Numerical results show that the initially induced plasmoid triggers a secondary tearing instability, which gradually fills the current sheet with plasmoids, as has also been observed in the non-relativistic case. We find the plasmoid-chain greatly enhances the reconnection rate, which becomes independent of the Lundquist number, when this exceeds a critical value. In addition, we show the distribution of plasmoid size becomes a power law. Since magnetic reconnection is expected to play an important role in various high energy astrophysical phenomena, our results can be used for explaining the physical mechanism of them.Comment: 10 pages, 9 figures, accepted for publication in Ap

Analysis of the Relaxation Process using Non-Relativistic Kinetic Equation

We study the linearized kinetic equation of relaxation model which was proposed by Bhatnagar, Gross and Krook (also called BGK model) and solve the dispersion relation. Using the solution of the dispersion relation, we analyze the relaxation of the macroscopic mode and kinetic mode. Since BGK model is not based on the expansion in the mean free path in contrast to the Chapman-Enskog expansion, the solution can describe accurate relaxation of initial disturbance with any wavelength. This non-relativistic analysis gives suggestions for our next work of relativistic analysis of relaxation.Comment: 18 pages, 14 figures, accepted for publication in Prog. Theor. Phys

Rapid cosmic-ray acceleration at perpendicular shocks in supernova remnants

Perpendicular shocks are shown to be rapid particle accelerators that perform optimally when the ratio $u_{\rm s}$ of the shock speed to the particle speed roughly equals the ratio $1/\eta$ of the scattering rate to the gyro frequency. We use analytical methods and Monte-Carlo simulations to solve the kinetic equation that governs the anisotropy generated at these shocks, and find, for $\eta u_{\rm s}\approx1$, that the spectral index softens by unity and the acceleration time increases by a factor of two compared to the standard result of diffusive shock acceleration theory. These results provide a theoretical basis for the thirty-year-old conjecture that a supernova exploding into the wind of a Wolf-Rayet star may accelerate protons to an energy exceeding $10^{15}\,$eV.Comment: 12 pages, 2 figures, accepted for publication in Ap

The Evolution of High Temperature Plasma in Magnetar Magnetospheres and its Implications for Giant Flares

In this paper we propose a new mechanism describing the initial spike of giant flares in the framework of the starquake model. We investigate the evolution of a plasma on a closed magnetic flux tube in the magnetosphere of a magnetar in the case of a sudden energy release and discuss the relationship with observations of giant flares. We perform one-dimensional numerical simulations of the relativistic magnetohydrodynamics in Schwarzschild geometry. We assume energy is injected at the footpoints of the loop by a hot star surface containing random perturbations of the transverse velocity. Alfv\'en waves are generated and propagate upward, accompanying very hot plasma that is also continuously heated by nonlinearly generated compressive waves. We find that the front edges of the fireball regions collide at the top of the tube with their symmetrically launched counterparts. This collision results in an energy release which can describe the light curve of initial spikes of giant flares.Comment: 13 pages, 11 figures, accepted for publication in Ap