Radiation-dominated polar emitting region of an accreting X-ray pulsar -- I. Polarization- and spectrum-dependent structure, and the emergent continuum

TL;DR

This paper presents a detailed numerical simulation of the radiation-dominated polar emitting region in an accreting X-ray pulsar, incorporating complex physical processes to understand its spectrum and polarization characteristics.

Contribution

It introduces a comprehensive 3D model including polarization-dependent scattering, Comptonization, and realistic magnetic field effects, advancing the understanding of X-ray pulsar emission mechanisms.

Findings

Induced Compton effect influences electron temperature in the post-shock zone.

Bulk motion and thermal effects create high-energy regions in the emitted spectrum.

The model highlights the role of shock-induced photon energization in spectral formation.

Abstract

The radiation-dominated polar emitting region of an accreting X-ray pulsar is simulated numerically in the framework of a three-dimensional (geometrically two-dimensional) model. The radiative transfer within the emitting region and the structure of the latter are calculated with the use of the self-consistent algorithm developed earlier. The magnetic scattering cross sections dependent on the photon energy and polarization have been incorporated. Second-order bulk Comptonization over entire emitting region, induced Compton scattering, the switching of the polarization modes, free-free processes, the cyclotron emission because of electron-proton collisions, and a realistic shape of the accretion channel have been taken into account. The case of a dipole magnetic field is considered. It is shown that the induced Compton effect can play a notable role in establishing the electron temperature in the post-shock zone. Within the model shock wave, a higher electron temperature is achieved than in the post-shock zone by means of the bulk-heating mechanism. The photons gaining the energy in the shock wave and above it due to bulk motion effects and the thermal Doppler effect are responsible for the formation of high-energy regions in the emergent continuum of the polarization modes.