66 research outputs found
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
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 of the shock speed to the particle speed
roughly equals the ratio 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
, 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
eV.Comment: 12 pages, 2 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
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
A new scheme of causal viscous hydrodynamics for relativistic heavy-ion collisions: A Riemann solver for quark-gluon plasma
In this article, we present a state-of-the-art algorithm for solving the
relativistic viscous hydrodynamics equation with the QCD equation of state. The
numerical method is based on the second-order Godunov method and has less
numerical dissipation, which is crucial in describing of quark-gluon plasma in
high-energy heavy-ion collisions. We apply the algorithm to several numerical
test problems such as sound wave propagation, shock tube and blast wave
problems. In sound wave propagation, the intrinsic numerical viscosity is
measured and its explicit expression is shown, which is the second-order of
spatial resolution both in the presence and absence of physical viscosity. The
expression of the numerical viscosity can be used to determine the maximum cell
size in order to accurately measure the effect of physical viscosity in the
numerical simulation.Comment: 38pages, 31 figures; published versio
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