CONTINUUM RADIATIVE-TRANSFER IN THE POLAR COLUMNS OF ACCRETION POWERED PULSARS - INCOHERENT-SCATTERING

We describe a new technique for studying the flow of radiation through one-dimensional slabs of the strongly magnetized thermal plasma in the polar regions of accreting, magnetized neutron stars. Our method allows rapid computation of one-dimensional model atmospheres with arbitrary orientation of the magnetic field with respect to the slab, as well as arbitrary inhomogeneity - we find improvements in computational speed by factors up to 105 in comparison with previously published algorithms. We include the effects of coherent and incoherent scattering in the continuum, bremsstrahlung emission and absorption, and a net continuum emissivity from the cyclotron line. We neglect the effect of velocity and velocity shear on the formation of the continuum, which restricts us to study the subsonic settling regions of flow onto a neutron star. We do not include the effects of vacuum polarization, since these are unlikely to be important in high density atmospheres expected to be present in the settling regions. Comptonization is assumed to be important only in regions where the radiation field is almost isotropic, which limits us to consideration of atmospheres whose Thomson optical depth exceeds ∼(mec2/Te)1/2 ≫ 1. We demonstrate this solution scheme with several models of emission from one-dimensional slabs representing parts of the photosphere of an X-ray pulsar.