ASCA Observations of SS Cyg

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Session 45 -- CVs/Symbiotic Stars
Display presentation, Wednesday, 1, 1994, 9:20-6:30

[45.01] ASCA Observations of SS Cyg

J. Nousek, C. Baluta (Penn State), K. Mukai (GSFC), J. Osborne (Leicester Univ.), M. Ishida (ISAS)

SS~Cygni was observed by the ASCA satellite on 27 May 1993, the first cataclysmic 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 with components of kT$=$0.8 and 5 keV, as invoked in previous studies with lower spectral resolution. Significantly better agreement is found for models with plasma emission at kT$=$0.8, 2.2 keV and thermal bremsstrahlung at kT$=$18 keV.

We interpret this result as evidence for a paucity of material emitting in the range near 5~keV. Such a deficit of intermediate temperature emission measure can be well reconciled with boundary layer models of the type presented by Narayan \& Popham. In such models the emission we see below 2~keV originates in the optically thick inner edge of the accretion disk, while the hard component comes in a narrow spike at the inner edge of the boundary layer. The optically thin part of the accretion disk provides little emission measure, which explains the deficit of 5~keV emitting material.

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.

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