Atmosphere Models of Magnetized Neutron Stars: QED Effects, Radiation Spectra and Polarization Signals

Abstract

Observations of surface emission from isolated neutron stars (NSs) provide unique challenges to theoretical modeling of radiative transfer in magnetized NS atmospheres. Recent work has demonstrated the critical role of vacuum polarization effects in determining NS spectra and polarization signals, in particular the conversion of photon modes (due to the “vacuum resonance” between plasma and vacuum polarization) propagating in the density gradient of the NS atmosphere. Previous NS atmosphere models incorporated the mode conversion effect approximately, relying on transfer equations for the photon modes. Such treatments are inadequate near the vacuum resonance, particularly for magnetic field strengths around B∼Bl≃7×1013 G, where the resonance occurs near the photosphere. In this proceeding, we describe our accurate treatment of the mode conversion effect in magnetized NS atmosphere models, employing both the modal radiative transfer equations coupled with the mode conversion probability at the vaccum resonance, and the full evolution equations for the photon Stokes parameters. In doing so, we are able to quantitatively calculate the effects of vacuum polarization on atmosphere structure, emission spectra, beam patterns, and polarizations for the entire range of magnetic field strengths, B = 1012−1015 G.