ASCA OBSERVATIONS OF SS CYGNI DURING AN ANOMALOUS OUTBURST

SS Cygni was observed by the ASCA satellite on 1993 May 27, the first catalysmic variable studied by ASCA. The observations were conducted while the system was in an outburst of the ''anomalous'' variety. The SIS spectrum cannot be explained by two-temperature Raymond-Smith coronal plasma models as invoked in previous studies with lower spectral resolution. Significantly better agreement is found for models with plasma emission at kT = 0.8, 3.5 keV and thermal bremsstrahlung at kT = 18 keV. The GIS data are consistent with the SIS data, showing evidence for Fe line emission but showing no evidence of pulsation over times ranging from seconds to minutes. These observations seem at variance with standard theory in two regards: we simultaneously see hard X-rays and optically thin soft X-rays while the system is in outburst, and we see a nonsmooth emission measure distribution. We speculate on possible scenarios which might resolve these differences.