Exosat and IUE observations of SW UMa during superoutburst

IUE and Exosat observations obtained during the March 1986 superoutburst of the SU UMa type dwarf nova SW UMa are presented. The observations show the presence of a hot, extensive, optically thick disk. The UV fluxes show an increase of 1000 over the quiescent values, implying a large increase in mass accretion rate. The Exosat obserations show an increase in the soft X-ray count rate by a factor of 44 over quiescence, while the medium-energy flux remains undetected. The most surprising result is that the softness ratio in superoutburst is similar to the quiescent value of 0.3. No variation at the orbital or spin periods or at the superhump period are evident in the superoutburst X-ray data. A transient variation is observed at 5.1 minutes similar to that observed in the optical a few days after the X-ray observations. 35 references