Identification of 1RXS J165424.6-433758 as a polar cataclysmic variable

Abstract

We present the results of our X-ray, ultraviolet, and optical follow-up campaigns of 1RXS J165424.6-433758, an X-ray source detected with the \textit{Swift} Deep Galactic Plane Survey (DGPS). The source X-ray spectrum (\textit{Swift} and \textit{NuSTAR}) is described by thermal bremsstrahlung radiation with a temperature of $kT=10.1\pm 1.2$ keV, yielding an X-ray ($0.3-10$ keV) luminosity $L_X=(6.5\pm 0.8)\times 10^{31}$ erg s${}^{-1}$ at a \textit{Gaia} distance of 460 pc. Spectroscopy with the Southern African Large Telescope (SALT) revealed a flat continuum dominated by emission features, demonstrating an inverse Balmer decrement, the $\lambda 4640$ Bowen blend, almost a dozen HeI lines, and HeII $\lambda 4541$, $\lambda 4686$ and $\hat{I}»5411$. Our high-speed photometry demonstrates a preponderance of flickering and flaring episodes, and revealed the orbital period of the system, $P_{\text{orb}}=2.87$ hr, which fell well within the cataclysmic variable (CV) period gap between $2-3$ hr. These features classify 1RXS J165424.6-433758 as a nearby polar magnetic CV.

Accepted for publication in ApJ