Hard X-ray properties of magnetic cataclysmic variables

Scaringi, S.; Bird, A. J.; Norton, A. J.; Knigge, C.; Hill, A. B.; Clark, D. J.; Dean, A. J.; McBride, V. A.; Barlow, E. J.; Bassani, L.; Bazzano, A.; Fiocchi, M. and Landi, R. (2010). Hard X-ray properties of magnetic cataclysmic variables. Monthly Notices of the Royal Astronomical Society, 401(4) pp. 2207–2218.

DOI: https://doi.org/10.1111/j.1365-2966.2009.15826.x

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 CV matches, and also present an additional nine (of which three 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 the Swift/BAT and SUZAKU/HXD in order to make our study more complete. We find that most hard X-ray-detected mCVs have Pspin/Porb < 0.1 above the period gap. In this respect, we also point out the very low number of detected systems in any band between Pspin/Porb= 0.3 and Pspin/Porb= 1 and the apparent peak of the Pspin/Porb distribution at about 0.1. The observational features of the Pspin–Porb 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 Pspin, Porb and Pspin/Porb . An attempt to explain the observed correlations is made in the context of mCV evolution and accretion footprint geometries on the white dwarf surface.

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