A Multiwavelength View of SPLUS J102139.31-282247.5: an X-ray Luminous and Eclipsing Dwarf Nova

Abstract

We report the independent discovery of the cataclysmic variable (CV) SPLUS J102139.31-282247.5 using Southern Photometric Local Universe Survey 12 band photometry, following its initial identification via ASAS-SN variability. Here, we investigate the system using optical photometry alongside optical and X-ray spectroscopy. High-cadence optical light curves from publicly available TESS data and a dedicated campaign at the Pico dos Dias Observatory in Brazil revealed a highly inclined system exhibiting pronounced eclipses with an orbital period of 1.81 hours. We found no evidence of a WD spin period. Despite seasonal gaps, the long-term ASAS-SN light curve revealed several outbursts (15 with $Δ$mag $\sim$ 1.5 brighter than the mean magnitude) and one superoutburst over the past decade. During Swift X-ray telescope observations, the system exhibited X-ray luminosity of $8.5 \times 10^{31}$ erg s$^{-1}$ in the 0.3-10\,keV band, originating from thermal plasma emission at a temperature consistent with accretion shocks. Optical spectroscopy from the Gemini Multi-Object Spectrographs on the Gemini South telescope confirms the CV nature of the system, showing strong, double-peaked H and HeI emission lines alongside a weak HeII4686 line. Altogether, these features strongly support the classification of SPLUS J102139.31-282247.5 as a quiescent, eclipsing dwarf nova with an unusually high X-ray luminosity.