Swift Deep Galactic Plane Survey Classification of Swift J170800$-$402551.8 as a Candidate Intermediate Polar Cataclysmic Variable

Here, we present the results of our multi-wavelength campaign aimed at classifying Swift J170800$-$402551.8 as part of the Swift Deep Galactic Plane Survey (DGPS). We utilized Target of Opportunity (ToO) observations with Swift, NICER, XMM-Newton, NuSTAR, and the Southern African Large Telescope (SALT), as well as multi-wavelength archival observations from Gaia, VPHAS, and VVV. The source displays a periodicity of 784 s in our XMM-Newton observation. The X-ray spectrum (XMM-Newton and NuSTAR) can be described by thermal bremsstrahlung radiation with a temperature of $kT$\,≈\,$30$ keV. The phase-folded X-ray lightcurve displays a double-peaked, energy-dependent pulse-profile. We used Chandra to precisely localize the source, allowing us to identify and study the multi-wavelength counterpart. Spectroscopy with SALT identified a Balmer H$?$ line, and potential HeI lines, from the optical counterpart. The faintness of the counterpart (r\,≈\,$21$ AB mag) favors a low-mass donor star. Based on these criteria, we classify Swift J170800$-$402551.8 as a candidate intermediate polar cataclysmic variable, where the spin period of the white dwarf is 784 s.