Identification of 1RXS J165424.6-433758 as a Polar Cataclysmic Variable

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 Swift Deep Galactic Plane Survey. The source X-ray spectrum (Swift and NuSTAR) is described by thermal bremsstrahlung radiation with a temperature of kT = 10.1 +/- 1.2 keV, yielding an X-ray (0.3-10 keV8) luminosity L X = (6.5 +/- 0.8) x 1031 erg s-1 at a Gaia distance of 460 pc. Spectroscopy with the Southern African Large Telescope revealed a flat continuum dominated by emission features, demonstrating an inverse Balmer decrement, the lambda 4640 Bowen blend, almost a dozen He i lines, and He ii lambda 4541, lambda 4686, and lambda 5411. Our high-speed photometry demonstrates a preponderance of flickering and flaring episodes, and revealed the orbital period of the system, P orb = 2.87 hr, which fell well within the cataclysmic variable (CV) period gap between 2 and 3 hr. These features classify 1RXS J165424.6-433758 as a nearby polar magnetic CV.

Automated summary

We present the results of our X-ray, ultraviolet, and optical follow-up campaigns of 1RXS J165424.6-433758, which is identified as a nearby polar magnetic cataclysmic variable (CV) based on its X-ray spectrum, emission features in the optical spectroscopy, and the orbital period.