An XMM-Newton timing analysis of the eclipsing polar DP Leo

Abstract

We present an analysis of the X-ray light curves of the magnetic cataclysmic variable DP Leo using recently performed XMM-Newton EPIC and archival ROSAT PSPC observations. We determine the eclipse length at X-ray wavelengths to be 235 +-5 s, slightly longer than at ultra-violet wavelengths, where it lasts 225s. The implied inclination and mass ratio for an assumed 0.6 M(sun) white dwarf are i=79.7 degrees and Q = M(wd)/M2 = 6.7. We determine a new linear X-ray eclipse and orbital ephemeris which connects the more than 120000 binary cycles covered since 1979. Over the last twenty years, the optical and X-ray bright phases display a continuous shift with respect to the eclipse center by \~2.1 degr/yr. Over the last 8.5 years the shift of the X-ray bright phase is \~2.5 degr/yr. We interpret this as evidence of an asynchronously rotating white dwarf although synchronization oscillations cannot be ruled out completely. If the observed phase shift continues, a fundamental rearrangement of the accretion geometry must occur on a time-scale of some ten years. DP Leo is marginally detected at eclipse phase. The upper limit eclipse flux is consistent with an origin on the late-type secondary, L_X ~ 2.5 x 10**(29) ergs/s (0.20-7.55 keV}), at a distance of 400 pc.