Multiwavelength Superoutburst Observations of T Leonis

Abstract

We present results of simultaneous superoutburst observations in the X-ray, EUV, optical, and IR bands of the tremendous outburst amplitude dwarf novae T Leonis. Near peak luminosity, a single blackbody represents a good fit to T Leo's observed continuum in the EUV spectral region, yielding a boundary layer temperature of 71,000-97,000 K. Inclusion of the longer wavelength observations, UV to the IR, indicates that a blackbody fit is inappropriate. A single-temperature fit to only the UV and redward data for T Leo works well but yields a much lower temperature, near 28,000 K. Using our own observations and previously obtained EUV, UV, and optical (super)outburst observations for the dwarf novae U Gem and SS Cyg, the SU UMa star VW Hyi, and the TOADs, TV Crv, BC UMa, and SW UMa, we find that in all cases, high-energy observations yield high-temperature, small emitting regions, while fits to UV and redward data produce cooler temperatures from much larger emitting regions. These results are consistent with the idea that high-energy data provide a direct measurement of the boundary layer, while the lower energy data measure a much larger, multitemperature region, likely to be dominated by the outburst heated inner accretion disk. High-energy outburst observations show that the boundary layer temperature decreases with decreasing orbital period, and UV outburst observations provide evidence for a missing or weak inner disk in the TOADs. We present a simple model of mass accretion onto the white dwarf during (super)outburst, which can account for the observed correlation between orbital period and boundary layer temperature.