Characterization of new hard X-ray Cataclysmic Variables

TL;DR

This study characterizes nine new hard X-ray selected Cataclysmic Variables, confirming all as Intermediate Polars with detailed timing, spectral analysis, and estimations of system parameters, revealing diverse accretion modes and spectral features.

Contribution

It provides the first orbital period estimates for several sources and confirms the presence of soft X-ray components and warm absorbers in a significant subset of IPs.

Findings

All sources are confirmed as Intermediate Polars.

Detection of soft X-ray components in some systems.

Approximately 30% of IPs show soft X-ray emission.

Abstract

We aim at characterizing a sample of 9 new hard X-ray selected Cataclysmic Variable (CVs), to unambiguously identify them as magnetic systems of the Intermediate Polar (IP) type. We performed timing and spectral analysis by using X-ray, and simultaneous UV and optical data collected by XMM-Newton, complemented with hard X-ray data provided by INTEGRAL and Swift. The pulse arrival time were used to estimate the orbital periods. The X-ray spectra were fitted using composite models consisting of different absorbing columns and emission components. Strong X-ray pulses at the White Dwarf (WD) spin period are detected and found to decrease with energy. Most sources are spin-dominated systems in the X-rays, though four are beat dominated at optical wavelengths. We estimated the orbital period in all system (except for IGR J16500-3307), providing the first estimate for IGR J08390-4833, IGR J18308-1232, and IGR J18173-2509. All X-ray spectra are multi-temperature. V2069 Cyg and RX J0636+3535 posses a soft X-ray optically thick component at kT 80 eV. An intense K_alpha Fe line at 6.4 keV is detected in all sources. An absorption edge at 0.76 keV from OVII is detected in IGR J08390-4833. The WD masses and lower limits to the accretion rates are estimated. We found all sources to be IPs. IGR J08390-4833, V2069 Cyg, and IGR J16500-3307 are pure disc accretors, while IGR J18308-1232, IGR J1509-6649, IGR J17195-4100, and RX J0636+3535 display a disc-overflow accretion mode. All sources show a temperature gradient in the post-shock regions and a highly absorbed emission from material located in the pre-shock flow which is also responsible for the X-ray pulsations. Reflection at the WD surface is likely the origin of the fluorescent iron line. There is an increasing evidence for the presence of a warm absorber in IPs. The addition of 2 systems to the subgroup of soft X-ray IPs confirms a \sim 30% incidence.