Mullard Space Science Laboratory

R. L. C. Starling
An observational study of central engines in AGN
2004 (supervisor: E. M. Puchnarewicz)

This thesis studies the central engines of Active Galactic Nuclei. I investigate the role of accretion discs in AGN by analysis of their multiwavelength observational properties, both in individual sources and in a sample of objects. Particular attention is paid to the interpretation of the big blue bump as thermal emission from an accretion disc. The X-ray properties of contrasting individual galaxies are studied from spectral and temporal data obtained with the XMM satellite.

Observational constraints on accretion disc viscosity values are obtained for a subset of the Palomar Green quasar sample. Limits on the viscosity parameter, alpha, assuming a standard Shakura-Sunyaev viscosity prescription, are derived for the sample using the variability in their optical lightcurves.

The role of an accretion disc in an unusual Seyfert 1 galaxy, RE J2248-511, is investigated taking a multiwavelength approach. I combine X-ray data from XMM with optical and ultraviolet spectrophotometry and infrared photometry to obtain the spectral energy distribution of an AGN which exhibits both broad optical emission lines (FWHM 3000 km/s) and a soft X-ray excess. I model the observed big blue bump as emission from an accretion disc to explore the physics of a disc within this system and determine the corresponding black hole mass. The results are discussed within the context of normal and narrow-line Seyfert 1 galaxies.

XMM data is also used to gain a deeper insight into the X-ray properties of the Seyfert 1 galaxy with LINER (low-ionisation nuclear emission-line region) characteristics, NGC 7213. The broad-band spectral energy distribution of this source gives an insight into accretion in the central regions of LINER galaxies.


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