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|Title:||Exosat observations of Seyfert type galaxies.|
|Authors:||Turner, Tracey Jane.|
|Presented at:||University of Leicester|
|Abstract:||Analysis and results are presented from EXOSAT observations of Seyfert type active galactic nuclei (AGN). The sample chosen for study axe 48 hard X-ray selected Seyfert type AGN including all 29 of the emission line AGN in the Piccinotti sample making this the largest such survey to date. EXOSAT, its detectors and methods of data analysis axe detailed, with emphasis on background subtraction techniques. One of the most important new results from EXOSAT data is the discovery that rapid variability (factor 2 over a few thousand seconds) is common in AGN. No evidence is found in the sample sources for any characteristic timescales of variability. Combining EXOSAT LE and ME data allowed us to obtain broad band X-ray spectra over the range 0.1-10 keV. Spectra in the ∼ 2-10 keV range are found to be well described by a simple power-law. The distribution of spectral indices across the sample can be approximated by a Gaussian distribution of mean a = 0.70 and a = 0.17. The spectra are not all consistent with this mean at the 90% confidence level and there must some intrinsic spread in AGN slopes. This spread can be constrained to 0.14. EXOSAT has also revealed a significant number of sources with complex soft X-ray spectra. These include spectra with a second spectral component at soft X-ray energies and sources with ''leaky" absorbing columns. Evidence that soft excess components occur in at least 50% of Seyfert type AGN, together with detection of rapid variability in the soft component provides the strongest support to date for an accretion disc model for AGN.|
|Rights:||Copyright © the author. All rights reserved.|
|Appears in Collections:||Theses, Dept. of Physics and Astronomy|
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