Hard X-ray luminosity functions of cataclysmic variables: joint Swift/BAT and Gaia data
Abstract
Cataclysmic variables (CVs) are the most numerous population among the Galactic objects emitting in hard X-rays. Most probably, they are responsible for the extended hard X-ray emission of the Galactic ridge and the central Galactic regions. Here, we consider the sample of CVs detected in the all-sky hard X-ray Swift/BAT survey, which were also detected by Gaia and thus have reliable distance estimates. Using these data, we derive accurate estimates for local number density per solar mass ($\rho _{\rm M} = 1.37^{+0.3}_{-0.16}. \times 10^{-5}\, {\rm M}_\odot ^{-1}$) and luminosity density per solar mass ($\rho _{\rm L} = 8.95^{+0.15}_{-0.1}\times 10^{26}$ erg s-1 M$_\odot ^{-1}$) for objects in the sample. These values appear to be in good agreement with the integrated Galactic ridge X-ray emission and nuclear stellar cluster luminosities. Analysis of the differential luminosity functions dρM/d(log10Lx) and dρL/d(log10Lx) confirms that there are two populations of hard X-ray-emitting CVs. Intermediate polars dominate at luminosities L > 1033 erg s-1, whereas non-magnetic CVs and polars are much more numerous but have lower luminosities on average. As a consequence, the contribution of these populations to the observed hard X-ray luminosity is almost equivalent.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- April 2022
- DOI:
- 10.1093/mnras/stac417
- arXiv:
- arXiv:2202.05809
- Bibcode:
- 2022MNRAS.511.4937S
- Keywords:
-
- accretion;
- accretion discs;
- methods: statistical;
- stars: novae;
- cataclysmic variables;
- X-rays: binaries;
- X-rays: diffuse background;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 10 pages, 4 figures, 4 tables. Accepted for publication in MNRAS