The Simultaneous Optical-to-X-ray Spectral Energy Distribution of Soft
  X-ray Selected AGN observed by Swift
  We report Swift observations of a sample of 92 bright soft X-ray selected
active galactic nuclei (AGN). This sample represents the largest number of AGN
observed to study the spectral energy distribution (SED) of AGN with
simultaneous optical/UV and X-ray data. The principal motivation of this study
is to understand the SEDs of AGN in the optical/UV to X-ray regime and to
provide bolometric corrections which are important in determining the Eddington
ratio L/Ledd. In particular, we rigorously explore the dependence of the UV-EUV
contribution to the bolometric correction on the assumed EUV spectral shape. We
find strong correlations of the spectral slopes alpha-x and alpha-UV with
L/Ledd. Although Narrow-Line Seyfert 1 galaxies (NLS1s) have steeper alpha-x
and higher L/Ledd than Broad-Line Seyfert 1 galaxies (BLS1s), their optical/UV
to X-ray spectral slopes alpha-ox and optical/UV slopes alpha-UV are very
similar. The mean SED of NLS1s shows that in general this type of AGN appears
to be fainter in the UV and at hard X-ray energies than BLS1s. We find a strong
correlation between alpha-x and alpha-UV for AGN with X-ray spectral slopes
alpha-x<1.6. For AGN with steeper X-ray spectra, both this relation and the
relation between alpha-x and L/Ledd break down. At alpha-x$\approx$1.6, L/Ledd
reaches unity. We note an offset in the alpha-UV - L/Ledd relation between
NLS1s and BLS1s. We argue that alpha-UV is a good estimator of L/Ledd and
suggest that alpha-UV can be used to estimate L/Ledd in high-redshift QSOs.
Although NLS1s appear to be highly variable in X-rays they only vary marginally
in the UV.
