VZ Sex: X-Ray Confirmation of Its Intermediate Polar Nature

Abstract

Abstract Intermediate polars are members of the cataclysmic variable binary stars. They are characterized by a moderately magnetized white dwarf accreting matter from a cool main-sequence companion star. In many cases, this accretion gives rise to a detectable X-ray emission. VZ Sex is an interesting X-ray source whose nature needs a robust confirmation. Here, we used archived XMM-Newton observations to assign the source to the intermediate polar class. We applied the Lomb–Scargle periodogram method to detect any relevant periodic feature in the 0.1–10 keV light curve and performed a spectral fitting of the X-ray spectrum in order to get information on the on-going accretion mechanism. By inspecting the periodogram, we detected a clear periodic feature at ≃20.3 minutes that we interpret as the spin period of the white dwarf. We additionally found the typical side bands expected as the consequence of the beat between the spin and the orbital period of ≃3.581 hr. The source is characterized by an unabsorbed flux of ≃2.98 × 10−12 erg cm−2 s−1 corresponding to an intrinsic luminosity of ≃7 × 1031 erg s−1 for a distance of ≃433 pc. The existence of such features allows us to classify VZ Sex as a clear member of the intermediate polar class. Furthermore, with the estimated WD spin, the ratio P spin/P orb is ≃0.09, i.e., consistent with that expected for a typical IP system above the period gap. In addition, the estimated intrinsic luminosity opens the possibility that a bridge linking the normally bright IPs to the faint population of sources does exist.