Characterization of New Hard X-ray Cataclysmic Variables
Abstract
Magnetic cataclysmic variables (mCVs) constitute a subgroup of the CV class: close binary systems in which a white dwarf (the primary) accretes from a Roche-lobe filling main-sequence mass donor (the secondary) and consequently emits in the X-ray. mCvs host an accreting white dwarfs (WD) with magnetic field strengths B ≥10e5 G. These systems are further subdivided in two groups, depending on the WD magnetic field intensity and degree of synchronism (Prot=ω/Porb=Ω). Those called Polars are synchronous mCVs showing signatures of strong magnetic fields (B ∼ 10-230 MG). The so-called intermediate polars (IPs) possess instead asynchronously rotating WDs (Pω << PΩ) and weakly magnetized WDs (B < 10 MG). Though mCVs represent a relatively small (∼20%) fraction of CVs, this number is rapidly increasing thanks to the recent hard X-ray surveys conducted by INTEGRAL and Swift above 20 keV. Hard X-ray mCVs (IPs) have the potential to be important contributors to the X-ray source population at low luminosities (∼10e30 -10e33 erg s^-1 ). They were proposed to be the major constituent of galactic ridge and galactic bulge X-ray emission. Therefore, they are also believed to have an important role in the X-ray luminosity function of other galaxies. We performed an X-ray follow-up campaign of a sample of new hard CV candidates detected above 20keV, aimed at characterizing their timing (spin period and orbital period) and spectral properties. Most of the sources are identified as IPs with spin-to-orbit period ratios of the order of 0.1. Spectral analysis reveals multiple components and complex absorptions from both cool and warm absorbing material. We discuss the results of their hard X-ray properties in terms of compact star masses. We also discuss in more detail the most interesting and peculiar cases.
- Publication:
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AAS/High Energy Astrophysics Division #13
- Pub Date:
- April 2013
- Bibcode:
- 2013HEAD...1312604B