Radiative properties of magnetic neutron stars with metallic surfaces and thin atmospheres. (arXiv:1208.6582v1 [astro-ph.HE])

Radiative properties of magnetic neutron stars with metallic surfaces and thin atmospheres. (arXiv:1208.6582v1 [astro-ph.HE]):
The goal of this work is to develop a simple analytic description of the
emission properties (spectrum and polarization) of the condensed, strongly
magnetized surface of neutron stars. We have improved the method of van
Adelsberg et al. (2005) (arXiv:astro-ph/0406001) for calculating the spectral
properties of condensed magnetized surfaces. Using the improved method, we
calculate the reflectivity of an iron surface at magnetic field strengths B
\sim (10^{12} - 10^{14}) G, with various inclinations of the magnetic field
lines and radiation beam with respect to the surface and each other. We
construct analytic expressions for the emissivity of this surface as functions
of the photon energy, magnetic field strength, and the three angles that
determine the geometry of the local problem. Using these expressions, we
calculate X-ray spectra for neutron stars with condensed iron surfaces covered
by thin partially ionized hydrogen atmospheres. We develop simple analytic
descriptions of the intensity and polarization of radiation emitted or
reflected by condensed iron surfaces of neutron stars with strong magnetic
fields typical for isolated neutron stars. This description provides boundary
conditions at the bottom of a thin atmosphere, which are more accurate than
previously used approximations. The spectra calculated with this improvement
show absorption features different from those in simplified models. The
approach developed in this paper yields results that can facilitate modeling
and interpretation of the X-ray spectra of isolated, strongly magnetized,
thermally emitting neutron stars.