The XMM-Newton view of the eclipse and dips of the dwarf nova Z Chamaleontis
A. A. Nucita1,2, E. Kuulkers3, B. M. T. Maiolo1, F. De Paolis1,2, G. Ingrosso1,2 and D. Vetrugno1,2
Department of PhysicsUniversity of Salento, via per Arnesano, CP 193, 73100, Lecce, Italy
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
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 FAbs0.2-9.0 = (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 LBolX = (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.
Key words: X-rays: binaries / white dwarfs / novae, cataclysmic variables
© ESO, 2011