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

TL;DR

This study identifies 1RXS J165424.6-433758 as a nearby polar magnetic cataclysmic variable through multi-wavelength observations, revealing its X-ray spectrum, optical emission features, and orbital period within the CV period gap.

Contribution

The paper provides the first comprehensive multi-wavelength characterization confirming the source as a polar CV with a precise orbital period.

Findings

X-ray spectrum consistent with thermal bremsstrahlung at 10.1 keV

Optical spectroscopy shows emission lines and inverse Balmer decrement

Orbital period of 2.87 hours within the CV period gap

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 $kT=10.1\pm1.2$ keV, yielding an X-ray ($0.3-10$ keV) luminosity $L_X=(6.5\pm0.8)\times10^{31}$ 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 $\lambda4640$ Bowen blend, almost a dozen HeI lines, and HeII $\lambda4541$, $\lambda4686$ and $\lambda 5411$. Our high-speed photometry demonstrates a preponderance of flickering and flaring episodes, and revealed the orbital period of the system, $P_\textrm{orb}=2.87$ 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.