A Particle Simulation for the Axisymmetric Pulsar Magnetosphere: II. the case of dipole field

TL;DR

This paper presents a detailed 3D particle simulation of an axisymmetric pulsar magnetosphere with a dipole magnetic field, analyzing plasma outflows and magnetic field modifications at low pair creation rates.

Contribution

It extends previous work by providing higher resolution simulations and analyzing the effects of pair creation and radiation drag on the magnetosphere structure.

Findings

Steady magnetosphere with outer gaps and plasma outflows.

Magnetic field remains close to dipole outside several light radii.

Pair creation influences plasma outflow and magnetic field configuration.

Abstract

The main issue of the pulsar magnetosphere is how the rotation power is converted into both particle beams which causes pulsed emissions, and a highly relativistic wind of electron-positron plasmas which forms surrounding nebulae shining in X-rays and TeV gamma-rays. As a sequel of the first paper (Wada & Shibata 2007), we carried out a three dimensional particle simulation for the axisymmetric global magnetosphere. We present the results of additional calculations, which are higher resolution model and higher pair creation rate cases, and a detailed analysis for the solution. We confined to demonstrate the cases of low pair creation rate, i.e., the magnetic field is fixed dipole. The radiation drag of the plasma is taken in a form with the curvature radius along the dipole magnetic field. The electrostatic interactions are calculated by a programmable special purpose computer, GRAPE-DR (Makino et al 2007). Once pair creation is onset in the outer gaps, the both signed particles begin to drift across the closed magnetic field due to radiation drag, and they create outflow. Eventually, the steady magnetosphere has outer gaps, both signed outflow of plasma and a region in which the electric field is dominant extending from the equator. In the steady state, the magnetic field made by magnetospheric current is comparable to the dipole magnetic field outside of several light radii from the star. In much more pair creation rate model, the effect of modification of the magnetic field will bring about modification of the outflow of the plasma, requiring further study with higher pair creation rate model in a subsequent paper.