Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........13t&link_type=abstract
PhD Dissertation, Pennsylvania State Univ. University Park, PA United States
Astronomy and Astrophysics
Astronomy
1
Accretion Disks, Active Galactic Nuclei, Seyfert Galaxies, Ultraviolet Emission, X Ray Spectra, Galactic Radiation, X Ray Sources, Black Holes (Astronomy), Heao 2, Iue, Rosat Mission, Infrared Spectra, Ultraviolet Spectra, Astronomical Models
Scientific paper
We survey the broadband spectral properties of approximately 500 x-ray selected Active Galactic Nuclei (AGN) observed with the Einstein X-ray Observatory. We find the mean spectral index of the AGN between 0.1 and 0.6 keV to be softer, and the distribution of indices wider, than previous estimates based on analyses of the x-ray spectra of optically-selected AGN. A correlation between radio and hard x-ray luminosity is confirmed, but the data do not support a correlation between radio loudness and soft x-ray spectral slope. Evidence for physically distinct soft and hard x-ray components is found. We observe subsamples of these AGN in the infrared, ultraviolet, and soft x-ray regions using the IRTF, IUE, and ROSAT observatories. The infrared data show the objects to be mainly point sources, with little extended emission. The UV data give measurements of strong emission lines (e.g., Ly-alpha, CIV, and CIII), along with measurements of the shape of the UV continuum. The ROSAT x-ray data allow accurate measurements of the soft x-ray slope and confirm the utility of our color-color spectral slope estimation procedure. Continuum measurements from these observations (in conjunction with optical data obtained by collaborators) are used for multiwavelength accretion disk modeling. Accretion disk modeling (making use of infrared, optical, ultraviolet, and soft x-ray data) is carried out on a sample of five Seyfert 1 galaxies possessing strong optical-ultraviolet-soft x-ray emission components. It is found that while bare accretion disk models cannot account for the soft x-ray emission observed in these objects, the addition of a hot, Comptonizing component enables the soft x-ray emission to be accounted for within the black hole plus accretion disk paradigm.
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