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Title: The spectral shape and variability of active galactic nuclei
Author: Hanson, Christopher Glen
ISNI:       0000 0001 3531 0138
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 1986
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We present the results of a study into the spectral shape and temporal variability of a number of active galactic nuclei. Quasi-simultaneous multi-frequency observations of the Seyfert galaxies NGC 5548 and NGC 4151 are presented. The radio to X-ray spectral shape in these sources seem to favours a synchrotron self-Compton model for the infrared and X-ray continua. The spectral flattening that is frequently seen shortward of ∼ 1 μm can be explained by the presence of thermal emission from an accretion disk. However, multi-temperature disk models are needed to fit the soft X-ray excess found in NGC 5548. It is also possible to interpret the soft X-ray excess in this source in terms of quasi-thermal emission from an electron-positron pair plasma. The variability characteristics of this source favour this interpretation. Multi-frequency observations of three blazars, Mrk 501, 3C 446 and OJ 287 can be most easily explained if the emission from these objects is dominated by emission from a relativistic jet aligned close to the line-of-sight. Mrk 501 seems unusually stable in its flux output compared to most other blazars. In contrast, both 3C 446 and OJ 287 were observed to undergo large intensity flares during the periods of our observations. Although the variability characteristics of 3C 446 are open to a number of interpretations, those of OJ 287 seem to favour the shock-wave model of Marscher & Gear (1985). Observations of a number of active galaxies with the Infrared Astronomical Satellite (IRAS) seem to indicate that a substantial part of the mid- to far-infrared emission from type 1 Seyfert galaxies, and probably also from radio-quiet quasars and broad-line radio galaxies, is due to thermal re-radiation from dust grains heated by the non-thermal optical and ultraviolet continua. A strong correlation between the luminosity in the narrow [0 III] λ 5007 emission line and the luminosities in the IRAS wavebands suggests that dust associated with the narrow-line region contributes significantly to the IRAS fluxes. A lack of variability found in the IRAS fluxes for some of the sources in our sample supports a thermal dust interpretation for the IRAS continua.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Astrophysics