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

We report the discovery of three 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 for 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 provides accurate localizations and spectral data for a broadband spectral analysis. All three objects were 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 greater than or similar to 18 keV for SRGA J194638.9+704552 and SRGA J225412.8+690658 and kT greater than or similar to 5 keV for SRGA J204547.8+672642. Together with the inferred high X-ray luminosities (2 x 10(32) -3 x 10(33) erg s(-1)), this strongly suggests that all three sources are cataclysmic variables (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 SRGA J194638.9+704552 is an intermediate polar, SRGA J204547.8+672642 is likely a polar or intermediate polar, and SRGA J225412.8+690658 is either a magnetic or nonmagnetic CV. We have also measured an orbital period of 2.98 h for SRGA J204547.8+672642 based on TESS data. Three out of the planned eight SRG all-sky surveys have now been completed. We expect to find many new CVs, in particular, magnetic systems, during the survey, and we plan to continue our optical follow-up program.

Automated summary

This study reports the discovery of three cataclysmic variables in the first year of the all-sky X-ray survey by the SRG orbital observatory. Through optical and X-ray analysis, their properties and characteristics are confirmed, and the orbital period of one of them is measured. This study is important for understanding the nature and distribution of cataclysmic variables.