A Combined Optical and X-ray Study of Unobscured Type 1 AGN. I. Optical
  Spectra and SED Modeling
  We present modeling and interpretation of the continuum and emission lines
for a sample of 51 unobscured Type 1 active galactic nuclei (AGN). All of these
AGNs have high quality spectra from both XMM-Newton and Sloan Digital Sky
Survey (SDSS). We extend the wavelength coverage where possible by adding
simultaneous UV data from the OM onboard XMM-Newton. Our sample is selected
based on low reddening in the optical and low gas columns implied by their
X-ray spectra. They also lack clear signatures for the presence of a warm
absorber. Therefore the observed characteristics of this sample are likely to
be directly related to the intrinsic properties of the central engine.
  We perform multi-component spectral fitting for strong optical emission lines
and the whole optical spectra. We fit the combined optical, UV and X-ray data
by applying a new broadband SED model which comprises the accretion disc
emission, low temperature optically thick Comptonisation and a hard X-ray tail
by introducing the a corona radius (Done et al. 2011). We find that in order to
fit the data, the model often requires an additional long wavelength optical
continuum component, whose origin is discussed in this paper. We also find that
the Photo-recombination edge of Balmer continuum shifts and broadens beyond the
standard limit of 3646{\AA}, implying an electron number density which is far
higher than that in the broad line region clouds.
  Our results indicate that the Narrow Line Seyfert 1s in this sample tend to
have lower black hole masses, higher Eddington ratios, softer 2-10 keV band
spectra, lower 2-10 keV luminosities and higher \alpha_{ox}, compared with
typical broad line Seyfert 1s (BLS1), although their bolometric luminosities
are similar. We illustrate these differences in properties by forming an
average SED for three subsamples, based on the FWHM velocity width of the
H{\beta} emission line.
