The Accretion Flow and Boundary Layer Structure in the Dwarf Nova SS Aur

We present X-ray analysis of dwarf novae SS Aur (51 ksec) using XMM-Newton Observatory archival data obtained in quiescence for a better understanding of the accretion flow structure. We find X-ray orbital modulations. We report power spectral analysis for EPIC (X-ray) and OM (UV) light curves suggesting high levels of red noise with no significant QPO or periodicities. We simultaneously fitted EPIC pn, MOS1 and MOS2 data using a model for interstellar medium absorption (tbabs) and a multi-temperature plasma emission model (cevmkl) as expected from low accretion rate quiescent dwarf novae. However, the composite model fit yields unacceptable reduced χ ^{2} values due to the existence of soft excess. The soft excess is well modeled using a blackbody model (kT∼∼24 eV) giving a better reduced χ ^{2} value over 3σ significance level. This may indicate the existence of optically thick boundary layer emission. We will discuss the origin of this excess. The best fitting model is a combination of a blackbody, a cevmkl and a power law with an interstellar absorption which yields a reduced χ ^{2} of 1.05. The fit also shows some oxygen and iron over abundances. SS Aur has a maximum thermal plasma temperature of ∼22 keV. The X-ray luminosity in the 0.1 to 50.0 keV energy band is ∼2.0×10 ^{33} ergs ^{-1}. Finally, we discuss these characteristics in the light of standard disk models and accretion flows and geometry in nonmagnetic cataclysmic variables.