THE X-RAY SPECTRAL ANALYSIS OF DWARF NOVA WZ Sge OBSERVED WITH ROSAT IN QUIESCENCE

Abstract

X-ray spectral parameters were determined for WZ Sge observed with the ROSAT PSPC. The raw data were fitted with various spectral models and the best fit spectral models are found to be that of Raymond–Smith and Thermal Bremsstrahlung. The best fit temperature was estimated to be kT ~ 2.17 keV while the column density was found to be NH ~ 2.8 × 1020 cm -2. The estimated 0.1–2.4 keV flux was in the range of log F = -12 ergs cm -2 s -1. WZ Sge stars show long outburst recurrence times and weak X-ray emissions during the quiescence states. It is possible to lengthen repetition cycles by decreasing the viscosity parameter (α); however there still remains the question why α is so small, specifically for these objects. The Coronal Siphon Model of Meyer and Meyer–Hofmeister1 can explain these phenomenons successfully. For this reason, the equations of this model were applied to the results of spectral analysis. Using this model, the mass accretion rate, mass evaporation rate in corona and the radius of the corona were calculated to be 1014.48 gr yr-1, 10-5.4 gr cm-2 s-1 and 109.7 cm, respectively. The obtained values suggest that the corona model can indeed operate in WZ Sge system.

XMM-NewtonandSwiftobservations of WZ Sagittae: spectral and timing analysis

“…Patterson et al (1998) described both the ROSAT and ASCA observations (as well as Einstein and EXOSAT ones) obtained in quiescence. This analysis was successively re-done by Gün (2005) who reported a quiescent 0.1-2.4 keV flux (as obtained from ROSAT PSPC in 1991) of 2.8 × 10 −12 erg cm −2 s −1 (corresponding to a luminosity of 6.3 × 10 29 erg s −1 for a distance of 43.5 pc). In addition, Hasenkopf & Eracleous (2002), reanalyzing a 1996 ASCA observation of WZ Sge, found a 0.5-10 keV flux of 4.7 × 10 −12 erg cm −2 s −1 , which implies a luminosity of 1.0 × 10 30 erg s −1 .…”