X-ray spectral analysis of SU UMa type Dwarf Novae observed with ROSAT

摘要

X-ray spectral parameters were determined for eight SU UMa type Dwarf Novae observed with the ROSAT PSPC. The raw data were fitted with various spectral models arid the best fit spectral models are found to be that of Raymond-Smith and Thermal Bremsstrahlung. The best fit temperatures were estimated to be between kT similar to1.1-1.8 keV while the Column Densities were found to be between N-H similar to2.4 x 10(20)-4.1 X 10(20) cm(-2). The estimated 0.1-2.4 keV fluxes were in the range of log F-X = -13 to -11 ergs cm(-2) s(-1). F-X/F-UV and F-X/F-opt rates were calculated to be between similar to0.09 and similar to0.37. This shows that most of the energy is radiated in the Optical and Ultraviolet band from the accretion disk in the quiescent state. Many of the SU UMa type Dwarf Novae show an Ultraviolet lag in their outburst spectrum, the Coronal Siphon Flow Model of Meyer and Meyer-Hofmeister may explain this phenomenon. This model proposes a corona at the boundary layer of a system when it is a quiescent state and suggests that some parts of the X-rays come from the corona. For these reasons, the equations of this model were applied to the results of the spectral analysis. Using this model, the mass accretion rates, the mass evaporation rates, and the radii of the coronas were calculated to be similar to10(-12.3)-10(-11.3) Mcircle dot yr(-1), similar to10(-6.5)-10(-5.5) g cm(-2) s(-1) and similar to10(9.1)-10(9.9) cm, respectively. The pressures in the coronas were less than similar to1200 g cm(-2) s(-1) for (z) up to similar to10 x 10(9) cm. The obtained values suggest that the Corona model can indeed operate in SU UMa type Dwarf Novae. [References: 30]