Computer Science
Scientific paper
Nov 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005phdt.........5e&link_type=abstract
PhD Thesis, University of Bristol, 2005.
Computer Science
1
Chandra, X-Ray
Scientific paper
In this thesis, I use X-ray, radio, and optical observations of radio galaxies to constrain the origin of their nuclear X-ray emission.
I present a detailed X-ray study of the nearest radio galaxy, Centaurus A, using new Chandra and XMM-Newton observations. For the first time in an FRI-type radio galaxy, I resolve fluorescent Fe Kalpha emission from cold, neutral, or near-neutral iron, which is consistent with an origin in a torus far from the central black hole. The continuum spectrum is well fitted with a combination of a heavily absorbed power-law component that is related to accretion phenomena, and an additional, less absorbed, power-law component that is associated with emission from the subparsec VLBI radio jet.
I present an in-depth analysis of the nuclear X-ray emission in the FRI radio galaxy NGC 6251, using X-ray data from Chandra and XMM-Newton, and supporting HST optical and VLBI radio data. I demonstrate that the nuclear spectral energy distribution and featureless X-ray continuum suggest that, unlike Centaurus A, the majority of X-ray emission arises from inverse-Compton upscattering of photons in the radio jet.
Finally, I examine the nuclear X-ray emission of a sample of 19 low-redshift (z<0.1) FRI- and FRII-type radio galaxies from the 3CRR catalog. I find correlations between the X-ray, radio, and optical fluxes and luminosities of X-ray components with low intrinsic hydrogen column densities, implying a common origin in the form of a jet. Several sources contain components with high intrinsic absorption whose X-ray luminosities are not as expected from the correlations, and are more likely to be accretion-dominated. For jet-dominated sources, I show that a hidden AGN component, obscured by a torus, is not excluded by the data, allowing the possibility of a model in which both components are present at varying levels in all radio galaxies. I also provide an in-depth discussion of the differing nuclear properties of FRI- and FRII-type sources, and for the first time demonstrate with X-ray data that an FRI/FRII dichotomy may exist on nuclear scales, as well as on extended scales.
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