Hard X-ray properties of magnetic cataclysmic variables

TL;DR

This study analyzes the hard X-ray properties of magnetic cataclysmic variables, revealing correlations with spin and orbital periods and providing insights into their evolution and accretion processes.

Contribution

It presents the first evidence of correlations between X-ray spectral hardness and spin/orbital periods in magnetic CVs, based on a comprehensive multi-instrument survey.

Findings

Most hard X-ray detected mCVs have P_{spin}/P_{orb}<0.1

Detected systems are scarce between P_{spin}/P_{orb}=0.3 and 1

Spectral hardness correlates with P_{spin}, P_{orb}, and their ratio

Abstract

Hard X-ray surveys have proven remarkably efficient in detecting intermediate polars and asynchronous polars, two of the rarest type of cataclysmic variable (CV). Here we present a global study of hard X-ray selected intermediate polars and asynchronous polars, focusing particularly on the link between hard X-ray properties and spin/orbital periods. To this end, we first construct a new sample of these objects by cross-correlating candidate sources detected in INTEGRAL/IBIS observations against catalogues of known CVs. We find 23 cataclysmic variable matches, and also present an additional 9 (of which 3 are definite) likely magnetic cataclysmic variables (mCVs) identified by others through optical follow-ups of IBIS detections. We also include in our analysis hard X-ray observations from Swift/BAT and SUZAKU/HXD in order to make our study more complete. We find that most hard X-ray detected mCVs have P_{spin}/P_{orb}<0.1 above the period gap. In this respect we also point out the very low number of detected systems in any band between P_{spin}/P_{orb}=0.3 and P_{spin}/P_{orb}=1 and the apparent peak of the P_{spin}/P_{orb} distribution at about 0.1. The observational features of the P_{spin} - P_{orb} plane are discussed in the context of mCV evolution scenarios. We also present for the first time evidence for correlations between hard X-ray spectral hardness and P_{spin}, P_{orb} and P_{spin}/P_{orb}. An attempt to explain the observed correlations is made in the context of mCV evolution and accretion footprint geometries on the white dwarf surface.