The XMM-Newton view of the eclipse and dips of the dwarf nova Z Chamaleontis

¹ Department of PhysicsUniversity of Salento, via per Arnesano, CP 193, 73100, Lecce, Italy
e-mail: nucita@le.infn.it
² INFN, Sez. di Lecce, via Per Arnesano, CP 193, 73100 Lecce, Italy
³ European Space Astronomy Centre, SRE-O, PO Box 78, 28691 Villanueva de la Cañada (Madrid), Spain

Received: 27 June 2011
Accepted: 25 September 2011

Abstract

Context. 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.

Aims. 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.

Methods. 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.

Results. 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 0.2–9.0 keV band is F^Abs_0.2-9.0 = (4.1±0.1) × 10^-12 erg s^-1 cm^-2, which, when accounted for absorption and bolometric correction, corresponds to a bolometric luminosity of L^Bol_X = (6.9±0.1) × 10³⁰  erg s^-1 at a distance of 97 pc. The mass accretion rate onto the white dwarf turns out to be about 1.1 × 10^-11M_⊙ yr^-1. 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 ± 0.003 count s^-1), 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.