Suzaku Observations of SS Cygni in Quiescence and Outburst

Abstract

Abstract We present results from the Suzaku observations of the dwarf nova SS Cyg in quiescence and outburst in 2005 November. The high sensitivity of the HXD PIN and the high spectral resolution of the XIS enabled us to determine the plasma parameters with unprecedented precision. The maximum temperature of the plasma in quiescence, 20.4$^{+4.0}_{-2.6}$(stat)$\pm$3.0(sys)keV, is significantly higher than that in outburst, 6.0$^{+0.2}_{-1.3}$keV. The elemental abundances are close to the solar ones for medium-$Z$ elements (Si, S, Ar), whereas they decline both in lighter and heavier elements, except for that of carbon, which is 2 solar, at least. The solid angle of the reflector subtending over an optically thin thermal plasma is $\Omega^{\rm Q}/(2\pi)$$=$ 1.7$\pm$0.2(stat)$\pm$0.1(sys) in quiescence. A 6.4 keV iron K$\alpha$ line is resolved into narrow and broad components. These facts indicate that both the white dwarf and the accretion disk contribute to the reflection. We consider the standard optically thin boundary layer as being the most plausible picture for the plasma configuration in quiescence. The solid angle of the reflector in outburst, $\Omega^{\rm O}\!\!/(2\pi)$$=$ 0.9$^{+0.5}_{-0.4}$, and a broad 6.4 keV iron line indicate that the reflection in outburst originates from the accretion disk and an equatorial accretion belt. The broad 6.4 keV line suggests that the optically thin thermal plasma is distributed on the accretion disk like solar corona.