Discovery of eRASSt J192932.9-560346: a bright, two-pole accreting, eclipsing polar

TL;DR

This paper reports the discovery and detailed characterization of a bright, eclipsing magnetic cataclysmic variable star, a polar, exhibiting two-pole accretion, strong polarization, and deep eclipses, identified through multi-wavelength observations.

Contribution

First identification of a bright, two-pole accreting polar with detailed polarization and eclipse analysis, linking X-ray and optical transient sources to a magnetic CV.

Findings

System is a two-pole accreting polar with a 92.5-minute orbital period.

Exhibits strong, variable circular and linear polarization confirming magnetic nature.

Deep eclipses and spectral features characterize the system's accretion geometry.

Abstract

We report the discovery of a bright (V ~ 15), eclipsing, two-pole accreting magnetic cataclysmic variable (CV), a polar, as counterpart of the eROSITA and Gaia transients eRASSt 192932.9-560346 and Gaia21bxo. Frequent large amplitude changes of its brightness at X-ray and optical wavelengths by more than 4 magnitudes was indicative of a CV nature of the source. Identification spectra obtained with the 10m SALT telescope revealed the typical features of a magnetic CV, strong, broad HeI, HeII and hydrogen Balmer emission lines superposed on a blue continuum. Time-resolved photoelectric polarimetry revealed circular polarization to vary from -20% to +20%, and linear polarization from 0% to 10% confirming the system to be magnetic CV of the polar subclass. High cadence photometry revealed deep, structured eclipses, indicating that the system is a two pole accretor. The orbital period determined from the eclipse times is 92.5094 +- 0.0002 min. The X-ray spectrum is thermal only and the implied luminosity is L_X=2.2 x 10^(31) erg/s at the Gaia-determined distance of 376 pc.