Sample of Cataclysmic Variables from 400d X-ray Survey

TL;DR

This paper identifies eight cataclysmic variables from the 400d X-ray survey and provides preliminary insights into their luminosity function at low X-ray luminosities, predicting thousands will be detected in future surveys.

Contribution

It presents the first sample of CVs from the 400d survey and constrains their low-luminosity X-ray luminosity function, highlighting differences from higher luminosity ranges.

Findings

The CV luminosity function slope is less steep at low luminosities.

Approximately a thousand CVs will be detected in future all-sky surveys.

Preliminary constraints on the low-luminosity X-ray luminosity function of CVs.

Abstract

We present a sample of eight cataclysmic variables (CVs) identified among the X-ray sources of the 400 square degree (400d) X-ray ROSAT/PSPC survey. Based on this sample, we have obtained preliminary constraints on the X-ray luminosity function of CVs in the solar neighbourhood in the range of low luminosities, L_X=~1e29-1e30 erg/s (0.5-2 keV). We show that the logarithmic slope of the CV luminosity function in this luminosity range is less steep than that at L_X>1e31 erg/s. Our results show that of order of thousand CVs will be detected in the SRG/eROSITA all-sky survey at high Galactic latitudes, which will allow to obtain much more accurate measurements of their X-ray luminosity function.