SIMBAD references

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 (ρ_M = 1.37^+0.3_–0.16. ×10^–5 M_☉^–1) and luminosity density per solar mass (ρ_L = 8.95^+0.15_–0.1×10²⁶ erg s^–1 M_☉^–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 dρ_M/d(log₁₀L_x) and dρ_L/d(log₁₀L_x) 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.