Breaking the degeneracy in magnetic cataclysmic variable X-ray spectral modeling using X-ray light curves

TL;DR

This paper demonstrates that combining X-ray light curves with spectral data can resolve parameter degeneracies in modeling magnetic cataclysmic variables, enabling more accurate determination of their fundamental properties.

Contribution

The study introduces an upgraded 3D modeling approach that incorporates light curves to break degeneracies in X-ray spectral fitting of magnetic cataclysmic variables.

Findings

X-ray light curves help break degeneracies in parameter estimation.

Spectral fitting alone can lead to incorrect parameter values.

Combining spectra and light curves improves fundamental parameter determination.

Abstract

We present an analysis of mock X-ray spectra and light curves of magnetic cataclysmic variables using an upgraded version of the 3D CYCLOPS code. This 3D representation of the accretion flow allows us to properly model total and partial occultation of the post-shock region by the white dwarf as well as the modulation of the X-ray light curves due to the phase-dependent extinction of the pre-shock region. We carried out detailed post-shock region modeling in a four-dimensional parameter space by varying the white dwarf mass and magnetic field strength as well as the magnetosphere radius and the specific accretion rate. To calculate the post-shock region temperature and density profiles, we assumed equipartition between ions and electrons, took into account the white dwarf gravitational potential, the finite size of the magnetosphere and a dipole-like magnetic field geometry, and considered cooling by both bremsstrahlung and cyclotron radiative processes. By investigating the impact of the parameters on the resulting X-ray continuum spectra, we show that there is an inevitable degeneracy in the four-dimensional parameter space investigated here, which compromises X-ray continuum spectral fitting strategies and can lead to incorrect parameter estimates. However, the inclusion of X-ray light curves in different energy ranges can break this degeneracy, and it therefore remains, in principle, possible to use X-ray data to derive fundamental parameters of magnetic cataclysmic variables, which represents an essential step toward understanding their formation and evolution.