SRGe J214919.3+673634—a Candidate for AM Her Variables Discovered by the eROSITA Telescope onboard the Spectrum–Roentgen–Gamma Orbital Observatory

Abstract

We present the results of the optical identification, classification, and analysis of our photometric and spectroscopic observations of the X-ray transient SRGe J214919.3+673634 discovered by the eROSITA telescope onboard the Spectrum–Roentgen–Gamma orbital observatory in the summer of 2021 during the fourth sky survey. The photometric observations of the optical counterpart of SRGe J214919.3+673634 performed at the 6-m BTA telescope of SAO RAS, the 1.5-m Russian–Turkish telescope RTT-150, and the 2.5-m telescope of CMO SAI MSU as well the archival data from the 48-inch ZTF telescope have shown that the source is a cataclysmic variable with an orbital period $P=85\pm 0.4$ min and exhibits a long-term photometric variability from $23.5^{m}$ (low state) to $20^{m}$ (high state). We show that the light curves in the high state are consistent with the model of an accreting magnetized white dwarf and suggest that SRGe J214919.3+673634 belongs to the AM Her variables. The spectra of the optical counterpart taken in the low state at BTA are consistent with the spectral energy distribution of a white dwarf with a temperature ${\sim}24\,000$ K.