X-ray emission from obscured Seyfert galaxies.

This thesis describes aspects of the X-ray emission from Seyfert 2 galaxies and the rather anomalous Seyfert 1 galaxy NGC 4151. A re-analysis of the Ginga observation of NGC 1068 is presented in Chapter 3. Its spectrum can be decomposed into four components, including Compton reflection possibly from an optically thick accretion disc and/or molecular torus. Reflection can account for all the iron emission-line radiation at 6.4 keV and increases the underlying power-law index to a 0.7, consistent with that seen in Seyfert 1 galaxies. Chapter 4 describes a re-analysis of the Ginga observations of 36 Seyfert 2 galaxies. The mean spectrum can be described by a power-law of index a ~ 1, reflection and absorption from cold gas. Thus the Ginga Seyfert 2's have a mean spectrum similar to Seyfert 1's, so supporting the predictions of the orientation dependent Seyfert unification schemes. There is an intrinsic dispersion within the sample, with several sources having an intrinsic index of a 1. These flat-spectrum sources have continua not easily understood in current thermal or non-thermal Comptonisation models, unless further extrinsic processes modify the hard X-ray spectra from these galaxies. In Chapter 5 the 0.1-300 keV properties of NGC 4151 axe presented based on a series of ROSAT, Asuka and OSSE observations. The ROSAT observations revealed a marked increase in the 1- 2 keV count-rate during a period of two days commencing approximately three days into the campaign. This soft X-ray variability is interpreted in terms of a change in the level of the hard X-ray continuum, and there is a good correspondence between the UV and soft X-ray light-curves. The observed UV/soft X-ray correlation is described in terms of a model in which the both reprocessing of the 0.1-300 keV continuum and gravitational energy release in the disc contribute to the observed UV emission.