A model for cyclotron resonance scattering features

TL;DR

This paper models the formation of cyclotron resonance scattering features in X-ray pulsars using Monte Carlo simulations, linking theoretical predictions with observational data to understand line shapes and geometries.

Contribution

It introduces a Monte Carlo-based model for cyclotron line formation that accounts for angle, geometry, and magnetic field variations, and applies it to observational data.

Findings

Predicted emission wings are not observed, suggesting a specific slab geometry.

Line shape depends on angle, optical depth, and temperature.

Model successfully fits RXTE and INTEGRAL data.

Abstract

(abbreviated version of the abstract) We study the physics of cyclotron line formation in the high-energy spectra of accreting X-ray pulsars using Monte Carlo methods, assuming that the line-forming region is a low-density electron plasma in a sub-critical magnetic field. We investigate the dependence of the shape of the fundamental line on angle, geometry, optical depth and temperature. We also discuss variations of the line ratios for non-uniform magnetic fields. These numerical predictions for the line profiles are linked to results from observational data analysis using an XSPEC model based on the Monte Carlo simulations. We apply this model to observational data from RXTE and INTEGRAL. The predicted strong emission wings of the fundamental cyclotron feature are not found in observational data, hinting at a bottom illuminated slab geometry for line formation.