Magnetic Thomson Transport in High Opacity Domains

TL;DR

This paper develops a semi-analytic approach to polarized magnetic Thomson radiative transfer in high opacity neutron star environments, improving simulation efficiency and understanding of radiation anisotropy and polarization.

Contribution

It introduces a reduced set of equations for high opacity magnetic Thomson scattering and provides empirical formulas for key parameters, enhancing modeling of neutron star atmospheres.

Findings

Derived compact equations for polarized scattering transport.

Provided empirical relations for anisotropy and polarization parameters.

Demonstrated faster scattering simulations using semi-analytic boundary conditions.

Abstract

X-ray radiation from neutron stars manifests itself in a variety of settings. Isolated pulsars, and magnetars both exhibit quasi-thermal persistent soft X-ray emission from their surfaces. Transient magnetospheric bursts from magnetars and pulsed signals from accreting neutron stars mostly appear in harder X rays. The emission zones pertinent to these signals are all highly Thomson optically thick so that their radiation anisotropy and polarization can be modeled using sophisticated simulations of scattering transport from extended emission regions. Validation of such codes and their efficient construction is enhanced by a deep understanding of scattering transport in high opacity domains. This paper presents a new analysis of the polarized magnetic Thomson radiative transfer in the asymptotic limit of high opacity. The integro-differential equations for photon scattering transport that result from a phase matrix construction are reduced to a compact pair of equations. This pair is then solved numerically for two key parameters that describe the photon anisotropy and polarization configuration of high Thomson opacity environs. Empirical approximations for these parameters as functions of the ratio of the photon and cyclotron frequencies are presented. Implementation of these semi-analytic transport solutions as interior boundary conditions is shown to speed up scattering simulations. The solutions also enable the specification of the anisotropic radiation pressure. The analysis is directly applicable to the atmospheres of magnetars and moderate-field pulsars, and to the accretion columns of magnetized X-ray binaries, and can be adapted to address other neutron star settings.