1995A&A...297L..55W

We report the detection of the bright QSO Ton S 180 by the Extreme Ultraviolet Explorer satellite during its all-sky survey. The measured count rate is 58cts/ksec, more than any other QSO or Sy-1 listed by the First EUVE Source Catalog. We have compiled previously unpublished optical, ultraviolet, and X-ray observations of this source, and construct the continuum spectral energy distribution. The soft X-ray range is well described by a single power law with spectral energy index α=-2.0. Although different ROSAT pointings show that the total X-ray counts have varied by a factor of 3, the shape of the spectrum has remained unchanged. The EUVE flux is fully compatible with the ROSAT survey measurement, confirming that the power law shape reaches well into the EUV regime. No additional soft X-ray or EUV excess could be found. The optical-UV continuum displays a strongly convex shape, with a turnover in νxf_ν already below 10eV. The overall shape of the continuum suggests that more than a single emission component contributes to the big blue bump.