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

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 SRGA J194638.9+704552 and SRGA J225412.8+690658 and kT 5 keV for SRGA J204547.8+672642. This, together with the inferred high X-ray luminosities (2 × 10 32 -3 × 10 33 erg s −1 ), strongly suggests that all 3 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 SRGA J194638.9+704552 is an intermediate polar, SRGA J204547.8+672642 is most likely a polar or an intermediate polar, and SRGA J225412.8+690658 can be either a magnetic or a non-magnetic CV. We also measured an orbital period of 2.98 hours 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 plenty of new CVs during the survey and to continue our optical follow-up program.