XMM-Newton observations of the dwarf nova YZ Cnc in quiescence

¹ Observatory, PO Box 14, 00014 University of Helsinki, Finland
² Mullard Space Science Lab, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
³ Department of Physics & Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK
⁴ Institute of Space Applications and Remote Sensing, National Observatory of Athens, PO Box 20048, Athens 11810, Greece
⁵ Institute of Astronomy & Astrophysics, National Observatory of Athens, PO Box 20048, Greece

Corresponding author: P. Hakala, pahakala@astro.helsinki.fi

Received: 10 December 2003
Accepted: 4 March 2004

Abstract

We present results from the XMM-Newton observations of the dwarf nova YZ Cnc in a quiescent state. We have performed a detailed time series analysis of the resulting light curves. Unusually, we do not detect any orbital modulation in the UV, with only marginal evidence for X-ray modulation on this period. Although there are peaks in the X-ray periodograms at periods less than 5000 s, we attribute them to red noise effects and assign significance to them using a novel approach. The variability in the UV and optical bands can also be modelled as a result of aperiodic variability (red noise) in the system. There is evidence that the UV and X-ray fluxes are anti-correlated with a time delay of about 100 s, with the UV lagging behind the X-ray emission. This anti-correlation is intriguing, but is only present on two occasions lasting several 1000 s each. The X-ray spectrum shows similar emission features to other dwarf novae and is well fitted using a multi-temperature emission model. We measure a relatively high X-ray luminosity of ergs/s, although this is consistent with a low binary inclination. Finally, we find evidence for a possible -1200 km s^-1 blue shift in the fitted Fe K line energies, possibly indicating the presence of an outflow in this low inclination system.