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

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.