The X-ray eclipse of the dwarf nova HT Cassiopeiae observed by the XMM-Newton satellite: spectral and timing analysis

¹ XMM-Newton Science Operations Centre, ESAC, ESA, PO Box 78, 28691 Villanueva de la , Madrid, Spain e-mail: anucita@sciops.esa.int
² Dipartimento di Fisica, Università del Salento, CP 193, 73100 Lecce, Italy
³ ESA, Research and Scientific Support Department, ESTEC, PO Box 299, 2200 AG, Noordwijk, The Netherlands
⁴ Integral Science Operations Centre, ESAC, ESA, PO Box 78, 28691 Villanueva de la , Madrid, Spain
⁵ Herschel Science Operations Centre, ESAC, ESA, PO Box 78, 28691 Villanueva de la , Madrid, Spain
⁶ INFN, Sezione di Lecce, via Arnesano, 73100 Lecce, Italy

Received: 2 December 2008
Accepted: 25 June 2009

Abstract

Context. A cataclysmic variable is a binary system consisting of a white dwarf that accretes material from a secondary object via the Roche-lobe mechanism. In the case of long enough observation, a detailed temporal analysis can be performed, allowing the physical properties of the binary system to be determined.

Aims. We present an XMM-Newton observation of the dwarf nova HT Cas acquired to resolve the binary system eclipses and constrain the origin of the X-rays observed. We also compare our results with previous ROSAT and ASCA data.

Methods. After the spectral analysis of the three EPIC camera signals, the observed X-ray light curve was studied with well known techniques and the eclipse contact points obtained.

Results. The X-ray spectrum can be described by thermal bremsstrahlung of temperature  keV plus a black-body component (upper limit) with temperature eV. Neglecting the black-body, the bolometric absorption corrected flux is  erg s^-1 cm^-2, which, for a distance of HT Cas of 131 pc, corresponds to a bolometric luminosity of  erg s^-1. In a standard accretion scenario where assuming , the amount of matter accreting onto the central white dwarf is found to be yr^-1. The study of the eclipse in the EPIC light curve permits us to constrain the size and location of the X-ray emitting region, which turns out to be close to the white dwarf radius. We measure an X-ray eclipse somewhat smaller (but only at a level of ) than the corresponding optical one. If this is the case, we have possibly identified the signature of either high latitude emission or a layer of X-ray emitting material partially obscured by an accretion disk.