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arXiv 0912.3582astro-ph.HE
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脉冲星磁层Y点的粒子模拟方法

Method of the Particle-in-Cell Simulation for the Y-point in the Pulsar Magnetosphere

Mitsuhiro Umizaki, Shinpei Shibata

摘要:

最近的X射线和伽马射线观测表明,脉冲星磁层的发射区可以是多重的。特别地,磁场的开-闭边界(所谓的Y点)可以是磁场能量转换成等离子体热和/或流动能量的新的候选位置。在这里,我们提出了一个新的Particle-in-Cell代码,它可以应用于轴对称几何中脉冲星磁层的Y点。电磁解算器用于具有圆柱坐标(R,z)的二维网格点,而粒子解算器在三维笛卡尔坐标(x,y,z)中操作,其中使用Buneman-Boris方法。粒子运动是用狭义相对论来处理的。利用Uzdensky(2003,ApJ,598,446)给出的无力半解析解,建立了产生磁层旋转的内边界条件。用正负电子等离子体中所有波模的色散关系对程序进行了验证。初步的测试运行也展示了Y形结构的顶部的死区上的轻圆柱。我们认为,结构是可变的准周期性与磁重联和等离子体将被加速和/或加热。从时间平均的观点来看,理想磁流体力学条件的破裂发生在Y点附近。

英文摘要:

Recent observations in X-ray and Gamma-ray suggest that the emission region of the pulsar magnetosphere can be multifold. In particular, the open-close boundary of the magnetic field, so-called the Y-point, can be the new candidate place where magnetic field energy converts into the plasma heat and/or flow energy. Here, we present a new Particle-in-Cell code, which can be applied to the Y-point of the pulsar magnetosphere in axisymmetric geometry. The electromagnetic solver is used in the two-dimensional grid points with the cylindrical coordinate (R, z), while the particle solver operates in the three-dimensional Cartesian coordinate (x, y, z), where the Buneman-Boris method is used. The particle motion is treated in special relativity. The inner boundary conditions are set up to generate rotation of the magnetosphere by use of the force-free semi-analytic solution given by Uzdensky (2003, ApJ, 598, 446). The code has been verified by dispersion relations of all the wave modes in electron-positron plasmas. The initial test run is also presented to demonstrate the Y-shaped structure at the top of the dead zone on the light cylinder. We suggest that the structure is variable with quasi-periodicity associated with magnetic reconnection and that plasma will be accelerated and/or heated. In a time-averaged point of view, break up of the ideal-MHD condition takes place in the vicinity of the Y-point.

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