Polarization properties of X-ray millisecond pulsars

TL;DR

This paper investigates the polarization of X-ray emissions from millisecond pulsars, analyzing scattering effects and predicting polarization properties to aid future observational tests of pulsar emission geometry.

Contribution

It introduces a relativistic rotation vector model to predict X-ray polarization and pulse profiles, incorporating effects of rapid rotation and light bending in millisecond pulsars.

Findings

Depolarizing effect of high electron temperature on single Compton scattering

Predicted polarization properties of nuclear- and accretion-powered millisecond pulsars

Relativistic rotation vector model including light bending effects

Abstract

Radiation of X-ray bursts and of accretion shocks in weakly magnetized neutron stars in low-mass X-ray binaries is produced in plane-parallel atmospheres dominated by electron scattering. We first discuss polarization produced by single (non-magnetic) Compton scattering, in particular the depolarizing effect of high electron temperature, and then the polarization due to multiply electron scattering in a slab. We further predict the X-ray pulse profiles and polarization properties of nuclear- and accretion-powered millisecond pulsars. We introduce a relativistic rotation vector model, which includes the effect of rotation of polarization plane due to the rapid motion of the hot spot as well as the light bending. Future observations of the X-ray polarization will provide a valuable tool to test the geometry of the emission region in pulsars and its physical characteristics.