THE SIMULTANEOUS OPTICAL-TO-X-RAY SPECTRAL ENERGY DISTRIBUTION OF SOFT X-RAY SELECTED ACTIVE GALACTIC NUCLEI OBSERVED BY SWIFT
- Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States)
- Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstr., D-85748 Garching (Germany)
- Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019 (United States)
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 {sub 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 {alpha}{sub X} and {alpha}{sub UV} with L/L {sub Edd}. Although narrow-line Seyfert 1 galaxies (NLS1s) have steeper {alpha}{sub X} and higher L/L {sub Edd} than broad-line Seyfert 1 galaxies (BLS1s), their optical/UV to X-ray spectral slopes {alpha}{sub ox} and optical/UV slopes {alpha}{sub 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 {alpha}{sub X} and {alpha}{sub UV} for AGNs with X-ray spectral slopes {alpha}{sub X}<1.6. For AGNs with steeper X-ray spectra, both this relation and the relation between {alpha}{sub X} and L/L {sub Edd} break down. At {alpha}{sub X}{approx}1.6, L/L {sub Edd} reaches unity. We note an offset in the {alpha}{sub UV}-L/L {sub Edd} relation between NLS1s and BLS1s. We argue that {alpha}{sub UV} is a good estimator of L/L {sub Edd} and suggest that {alpha}{sub UV} can be used to estimate L/L {sub Edd} in high-redshift QSOs. Although NLS1s appear to be highly variable in X-rays, they only vary marginally in the UV.
- OSTI ID:
- 21301227
- Journal Information:
- Astrophysical Journal, Supplement Series, Vol. 187, Issue 1; Other Information: DOI: 10.1088/0067-0049/187/1/64; Country of input: International Atomic Energy Agency (IAEA); ISSN 0067-0049
- Country of Publication:
- United States
- Language:
- English
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