R. J. Mitchell
Extragalactic X-ray astronomy
1976 (supervisor: J. L. Culhane)

The major part of this thesis concerns the analysis of data obtained from two satellites: COPERNICUS and ARIEL 5. Chapter 2 deals with variability of X-ray flux from Centaurus A, a compact and heavily absorbed source which was seen to have increased in brightness by a factor of 4 since the UHURU observation made two years earlier. Two chapters, numbers 3 and 4, are devoted to the Perseus cluster of galaxies, for which spatial and spectral aspects are discussed. An image reconstruction programme has been developed and applied to the COPERNICUS observations of the cluster core; this has revealed a North-South elongation similar to the radio structure as well as a steep flux gradient to the East of NGC 1275 corresponding to the termination of the chain of galaxies. ARIEL 5 observations have, by the discovery of Fe XXV and Fe XXVI, confirmed the thermal nature of the source (or, at least a component of the source) and enabled the abundance of iron in the cluster to be determined.

The Centaurus cluster is the subject of chapter 5. Observed features include a centrally condensed source showing no significant absorption, and evidence for possible iron line emission. In chapter 6 emission mechanisms associated with clusters are considered in relation to observations. An adiabatic model is discussed and the velocity dispersion-luminosity relationship is critically analysed.

Chapter 7 describes an experiment which utilised Bragg reflection techniques to search for line emission from a supernova remnant. Although originally designed to make a study of Cassiopeia A, the experiment in a similar form may also be employed to observe the brightest clusters of galaxies. The thesis commences with a short review of extragalactic X-ray astronomy.