Dynamical and Radiative Properties of X-ray Pulsar Accretion Columns: Phase-Averaged Spectra

Abstract

The availability of the unprecedented spectral resolution provided by modern X-ray observatories is opening up new areas for study involving the coupled formation of the continuum emission and the cyclotron absorption features in accretion-powered X-ray pulsar spectra. Previous research focusing on the dynamics and the associated formation of the observed spectra has largely been confined to the single-fluid model, in which the super-Eddington luminosity inside the column decelerates the flow to rest at the stellar surface, while the dynamical effect of gas pressure is ignored. In a companion paper, we have presented a detailed analysis of the hydrodynamic and thermodynamic structure of the accretion column obtained using a new self-consistent model that includes the effects of both gas and radiation pressure. In this paper, we explore the formation of the associated X-ray spectra using a rigorous photon transport equation that is consistent with the hydrodynamic and thermodynamic structure of the column. We use the new model to obtain phase-averaged spectra and partially-occulted spectra for Her X-1, Cen X-3, and LMC X-4. We also use the new model to constrain the emission geometry, and compare the resulting parameters with those obtained using previously published models. Our model sheds new light on the structure of the column, the relationship between the ionized gas and the photons, the competition between diffusive and advective transport, and the magnitude of the energy-averaged cyclotron scattering cross section.

Accepted for Publication in the Astrophysical Journal

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• A New Two-Fluid Radiation-Hydrodynamical Model for X-ray Pulsar Accretion Columns
• Dynamics of Neutron Star Accretion Columns in Split-Monopole Magnetic Fields
• A Bayesian approach for torque modelling of BeXRB pulsars with application to super-Eddington accretors
• Simulating the shock dynamics of a neutron star accretion column
• Three-dimensional modelling of accretion columns: spatial asymmetry and self-consistent simulations
• Radiative MHD Simulations of Photon Bubbles in Radiation-Supported Magnetized Atmospheres of Neutron Stars with Isotropic Thomson Scattering
• The giant outburst of 4U 0115+634 in 2011 with Suzaku and RXTE
• Vacuum polarization alters the spectra of accreting X-ray pulsars
• The giant outburst of EXO 2030+375 I: Spectral and pulse profile evolution
• Orbital- and spin-phase variability in the X-ray emission from the accreting pulsar Cen X-3
• Two-temperature accretion flows around strongly magnetized stars and their spectral analysis
• Hydrodynamical simulation of the structure of the X-ray pulsar accretion channel: accounting for resonant scattering
• Don't torque like that. Measuring compact object magnetic fields with analytic torque models
• Flux variability of the "10 keV feature" of 4U 0115+63