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

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.

42 pages, accepted for publication in The Astrophysical Journal Supplement Series

References in corpus (16)

• Magnetic White Dwarfs
• Magnetic fields in isolated and interacting white dwarfs
• The gas-to-extinction ratio and the gas distribution in the Galaxy
• The Accretion Flows and Evolution of Magnetic Cataclysmic Variables
• Measuring the masses of magnetic white dwarfs: A NuSTAR Legacy Survey
• Broad-band characteristics of seven new hard X-ray selected cataclysmic variables
• X-ray reflection from cold white dwarfs in magnetic cataclysmic variables
• Magnetic dynamos in white dwarfs -- I. Explaining the dearth of bright intermediate polars in globular clusters
• Spectroscopic Observations of the Intermediate Polar EX Hydrae in Quiescence
• Testing the cooling flow model in the intermediate polar EX Hydrae
• On the area of accretion curtains from fast aperiodic time variability of the intermediate polar EX Hya
• Constraining the accretion geometry of the intermediate polar EX Hya using NuSTAR, Swift and Chandra observations
• Influence of Compton scattering on the broad-band X-ray spectra of intermediate polars
• Stokes imaging of AM Her systems using 3D inhomogeneous models - I. Description of the code and an application to V834 Cen
• Accretion column structure of magnetic cataclysmic variables from X-ray spectroscopy
• The effect of two-temperature post-shock accretion flow on the linear polarization pulse in magnetic cataclysmic variables