GINGA Observation of SS Cygni

An X-ray observation of SS Cygni, a U Gem-type dwarf nova, was made with Ginga. The observed energy spectrum is well reproduced by a thermal bremsstrahlung spectrum including an iron emission line. However, the line center energy, 6.68+/-0.12 keV, is inconsistent with the plasma temperature, 17.5(+1.2}_{-1.0) keV, derived from the continuum spectrum if the X-ray emitting plasma is isothermal and in an ionization equilibrium. Possible explanations for this inconsistency are examined, and a two-temperature model for the hot plasma is proposed. Brief arguments are given for a possible geometry of the hot plasma and for the mass of the white dwarf in SS Cyg.