2010ApJS..187...64G

We report Swift observations of a sample of 92 bright soft X-ray selected active galactic nuclei (AGNs). This sample represents the largest number of AGNs observed to study the spectral energy distribution (SED) of AGNs with simultaneous optical/UV and X-ray data. The principal motivation of this study is to understand the SEDs of AGNs in the optical/UV to X-ray regime and to provide bolometric corrections which are important in determining the Eddington ratio L/L_Edd. 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 α_X and α_UV with L/L_Edd. Although narrow-line Seyfert 1 galaxies (NLS1s) have steeper α_X and higher L/L_Eddthan broad-line Seyfert 1 galaxies (BLS1s), their optical/UV to X-ray spectral slopes α_ox and optical/UV slopes α_UV are very similar. The mean SED of NLS1s shows that in general this type of AGNs appears to be fainter in the UV and at hard X-ray energies than BLS1s. We find a strong correlation between α_Xand α_UV for AGNs with X-ray spectral slopes α_X<1.6. For AGNs with steeper X-ray spectra, both this relation and the relation between α_X and L/L_Edd break down. At α_X ≈ 1.6, L/L_Eddreaches unity. We note an offset in the α_UV-L/L_Edd relation between NLS1s and BLS1s. We argue that α_UV is a good estimator of L/L_Eddand suggest that α_UV can be used to estimate L/L_Eddin high-redshift QSOs. Although NLS1s appear to be highly variable in X-rays, they only vary marginally in the UV.