We are conducting an archival Swift program to measure multiwavelength variability in active galactic nuclei (AGN). This variability information will provide constraints on the geometry, physical conditions and processes of the structures around the
central black holes that emit and reprocess the observed flux. Among our goals are: (1) to produce a catalog of type 1 AGN with time-resolved multi-wavelength data; (2) to characterize variability in the optical, UV and X-ay bands as well as changes in spectral slope; (3) to quantify the impact of variability on multi-wavelength properties; and (4) to measure correlated variability between bands. Our initial efforts have revealed a UVOT calibration issue that can cause a few percent of measured UV fluxes to be anomalously low, by up to 30%.
We have defined a sample of 63 AGN with strong forbidden high-ionisation line (FHIL) emission. These lines, with ionisation potentials >~ 100eV, respond to a portion of the spectrum that is often difficult to observe directly, thereby providing const
raints on the EUV-soft X-ray continuum. The sources are selected from the Sloan Digital Sky Survey (SDSS) on the basis of their [Fe X]6374A emission, yielding one of the largest and the most homogeneous sample of FHIL-emitting galaxies. We fit a sequence of models to both FHILs ([Fe XI], [Fe X] and [Fe VII]) and lower-ionisation emission lines ([O III], [O I], H-alpha, [N II], [S II]) in the SDSS spectra. These data are combined with X-ray measurements from Rosat, which are available for half of the sample. The correlations between these parameters are discussed for both the overall sample and subsets defined by spectroscopic classifications. The primary results are evidence that: (1) the [Fe X] and [Fe XI] lines are photoionised and their strength is proportional to the continuum flux around 250 eV; (2) the FHIL-emitting clouds form a stratified outflow in which the [Fe X] and [Fe XI] source regions extend sufficiently close to the BLR that they are partially obscured in Seyfert 2s whereas the [Fe VII] source region is more extended and is unaffected by obscuration; (3) narrow-lined Seyfert 1s (NLS1s) tend to have the strongest [Fe X] flux (relative to lower-ionisation lines); and (4) the most extreme [Fe X] ratios (such as [Fe X]/[O III] or [Fe X]/[Fe VII]) are found in the NLS1s with the narrowest broad lines and appear to be an optical-band indication of objects with strong X-ray soft excesses.
