XMM-Newton and Swift observations of WZ Sagittae: spectral and timing analysis

Context. WZ Sagittae is the prototype object of a subclass of dwarf novae with rare and long (super) outbursts, in which a white dwarf primary accretes matter from a low mass companion. High-energy observations offer the possibility of a better understanding of the disk-accretion mechanism in WZ Sge-like binaries. Aims. We used archival XMM-Newton and Swift data to characterize the X-ray spectral and temporal properties of WZ Sge in quiescence. Methods. We performed a detailed timing analysis of the simultaneous X-ray and UV light curves obtained with the EPIC and OM instruments on board XMM-Newton in 2003. We employed several techniques in this study, including a correlation study between the two curves. We also performed an X-ray spectral analysis using the EPIC data and Swift/XRT data obtained in 2011. Results. We find that the X-ray intensity is clearly modulated at a period of similar or equal to 28.96 s, confirming previously published preliminary results. We find that the X-ray spectral shape of WZ Sge remains practically unchanged between the XMM-Newton and Swift observations. However, after correcting for interstellar absorption, the intrinsic luminosity is estimated to be L-X(Una) = (2.65 +/- 0.06) x10(30) erg s(-1) and L-X(Una) = (1.57 +/- 0.03) x10(30) erg s(-1) in 2003 and 2011, respectively. During the Swift/XRT observation, the observed flux is a factor similar or equal to 2 lower than that observed by XMM-Newton but is similar to the quiescent levels that are observed various times before the 2001 outburst.