A Simple Model of Radiation from a Magnetized Neutron Star: Accreted Matter and Polar Hotspots

TL;DR

This paper refines a simple model of thermal radiation from magnetized neutron stars, showing that surface temperature distribution and polar heating can explain observed spectra regardless of envelope composition.

Contribution

It introduces a straightforward extension to existing models by incorporating polar heating, aligning theoretical predictions with observational data.

Findings

Thermal emission is largely independent of envelope composition.

Adding polar heating reproduces observed spectra of isolated neutron stars.

Surface temperature distribution is anisotropic due to magnetic field effects.

Abstract

A simple and well known model for thermal radiation spectra from a magnetized neutron star is further studied. The model assumes that the star is internally isothermal and possesses dipole magnetic field (B <= 1e14 G) in the outer heat-insulating layer. The heat transport through this layer makes the surface temperature distribution anisotropic; any local surface element is assumed to emit a blackbody (BB) radiation with a local effective temperature. It is shown that this thermal emission is nearly independent of the chemical composition of insulating envelope (at the same taken averaged effective surface temperature). Adding a slight extra heating of magnetic poles allows one to be qualitatively consistent with observations of some isolated neutron stars.