2011A&A...536A..75N

A cataclysmic variable contains a white dwarf that accretes material from a secondary star via the Roche lobe mechanism. Systems with high line-of-sight inclination angles offer the possibility to pinpoint the location of the X-ray emitting region by characterizing the observed eclipse by the secondary star. We present an XMM-Newton observation of the dwarf nova Z Chamaleontis that we analyzed to determine the properties of the X-ray and optical light curves, as well as the high-energy spectrum. We performed a spectral analysis of the data taken by the EPIC camera, and a timing analysis of the observed X-ray and optical OM light curves. We find that a multi-temperature plasma component absorbed by ionized material is required to describe the data. In particular, we estimate that the total absorbed flux in the 0.2-9.0keV band is F^Abs_0.2–9.0=(4.1±0.1)x10^–12erg/s/cm², which, when accounted for absorption and bolometric correction, corresponds to a bolometric luminosity of L^Bol_X=(6.9±0.1)x10³⁰erg/s at a distance of97 pc. The mass accretion rate onto the white dwarf turns out to be about 1.1x10^–11M_☉/yr. Our analysis of the optical and X-ray eclipse light curves and the mid-eclipse times of Z-Chamaleontis, in addition to the eclipse (during which the observed EPIC count rate is 0.033±0.003count/s), implies that the X-ray light curve contains dips (at the orbital phases 0.30±0.02 and 0.73±0.02) that can be naturally explained as absorption effects by intervening stable gas clouds close to the accretor.