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 kT_1=6.89 ± 0.23 keV plus a black-body component (upper limit) with temperature kT_2=30-6+8 eV. Neglecting the black-body, the bolometric absorption corrected flux is F{Bol}=(6.5± 0.1) × 10-12 erg s-1 cm-2, which, for a distance of HT Cas of 131 pc, corresponds to a bolometric luminosity of (1.33± 0.02) × 1031 erg s-1. In a standard accretion scenario where L_BL≃ 0.125 L_acc assuming Ω _WD ≃ 0.5 Ω_K(R_WD), the amount of matter accreting onto the central white dwarf is found to be 1.7 × 10 -11 Mȯ 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 ≃1.5 σ) 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.
The X-ray eclipse of the dwarf nova HT Cassiopeiae observed by the XMM-Newton satellite: spectral and timing analysis
NUCITA, Achille;MAIOLO, BERLINDA MARIA TERESA;DE PAOLIS, Francesco;INGROSSO, Gabriele
2009-01-01
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 kT_1=6.89 ± 0.23 keV plus a black-body component (upper limit) with temperature kT_2=30-6+8 eV. Neglecting the black-body, the bolometric absorption corrected flux is F{Bol}=(6.5± 0.1) × 10-12 erg s-1 cm-2, which, for a distance of HT Cas of 131 pc, corresponds to a bolometric luminosity of (1.33± 0.02) × 1031 erg s-1. In a standard accretion scenario where L_BL≃ 0.125 L_acc assuming Ω _WD ≃ 0.5 Ω_K(R_WD), the amount of matter accreting onto the central white dwarf is found to be 1.7 × 10 -11 Mȯ 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 ≃1.5 σ) 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
