Pulsed and Polarized X-ray Emission from Neutron Star Surfaces

TL;DR

This paper presents Monte Carlo simulations of polarized X-ray emission from neutron star surfaces, accounting for magnetic fields and general relativity, to interpret observed pulse profiles and constrain stellar geometry.

Contribution

It introduces a complex electric field vector formalism for polarized radiative transfer in neutron star atmospheres, incorporating relativistic effects to predict pulse profiles.

Findings

Constraints on neutron star geometry angles derived from observations.

Predictions of pulse profiles at different X-ray energies for magnetars and pulsars.

Insights into hot spot sizes and magnetic field configurations.

Abstract

The intense magnetic fields of neutron stars naturally lead to strong anisotropy and polarization of radiation emanating from their surfaces, both being sensitive to the hot spot position on the surface. Accordingly, pulse phase-resolved intensities and polarizations depend on the angle between the magnetic and spin axes and the observer's viewing direction. In this paper, results are presented from a Monte Carlo simulation of neutron star atmospheres that uses a complex electric field vector formalism to treat polarized radiative transfer due to magnetic Thomson scattering. General relativistic influences on the propagation of light from the stellar surface to a distant observer are taken into account. The paper outlines a range of theoretical predictions for pulse profiles at different X-ray energies, focusing on magnetars and also neutron stars of lower magnetization. By comparing these models with observed intensity and polarization pulse profiles for the magnetar 1RXS J1708-40, and the light curve for the pulsar PSR J0821-4300, constraints on the stellar geometry angles and the size of putative polar cap hot spots are obtained.