Identification of 3 cataclysmic variables detected by the ART-XC and eROSITA telescopes aboard SRG during the all-sky X-ray survey

TL;DR

This paper reports the discovery and characterization of three new cataclysmic variables detected by the SRG all-sky X-ray survey, using data from ART-XC and eROSITA telescopes, complemented by optical observations.

Contribution

It presents the identification of three previously unknown CVs from SRG survey data, including their spectral and optical properties, and classifies their types for the first time.

Findings

All three sources are confirmed as CVs based on X-ray spectra and optical data.

The sources exhibit high X-ray luminosities and thermal spectra consistent with CVs.

Orbital period of 2.98 hours measured for one source from TESS data.

Abstract

We report the discovery of three previously unknown cataclysmic variables in the data of the first year of the all-sky X-ray survey by the SRG orbital observatory. The sources were selected due to their brightness in the 4--12 keV band in the data of the Mikhail Pavlinsky ART-XC telescope. They are also detected by the eROSITA telescope, which provided accurate localizations and spectral data for broad-band spectral analysis. All three objects had been previously known as X-ray sources from the ROSAT all-sky survey and XMM-Newton slew survey, but their nature remained unknown. The X-ray spectra obtained by eROSITA and ART-XC are consistent with optically thin thermal emission with a temperature kT>~15 keV for SRGAJ194638.9+704552 and SRGAJ225412.8+690658 and kT>~5 keV for SRGAJ204547.8+672642. This, together with the inferred high X-ray luminosities ($2\times 10^{32}$-$3\times 10^{33}$ erg s$^{-1}$), strongly suggests that all three sources are CVs. We have obtained optical photometry and spectroscopy for these objects using the AZT-33IK 1.6-m telescope of the Sayan Observatory. The optical properties confirm the CV nature of the objects. We conclude that SRGAJ194638.9+704552 is an intermediate polar, SRGAJ204547.8+672642 is most likely a polar or an intermediate polar, and SRGAJ225412.8+690658 can be either a magnetic or a non-magnetic CV. We also measured an orbital period of 2.98~hours for SRGAJ204547.8+672642, based on TESS data. Three out of the planned eight SRG all-sky surveys have now been completed. We expect to find plenty of new CVs during the survey and to continue our optical follow-up program.