Galactic X-ray astronomy with EXOSAT

• Main Author: Norton, Andrew John
• Published: University of Leicester 1988
• Subjects: 523.01; Astrophysics
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233688

The work presented in this thesis covers two topics: a study of Intermediate Polars (non- synchronously rotating magnetic cataclysmic variables) and a survey of the Galactic plane, both carried out with the EXOSAT observatory. The first part of the thesis describes a study of all the Intermediate Polars observed by EXOSAT. The X-ray light curves and spectra of each source are considered, with particular emphasis on the spin modulation. By treating the Intermediate Polars as an homogenous set of objects, a model for the accretion flow and emission region is developed in which the modulation is due to a combination of photo-electric absorption and occultation effects. The modulation seen can be explained in terms of a single, large emission area in the vicinity of the magnetic pole of the white dwarf. Further analysis is presented concerning the differences in the observed properties of GK Per, between outburst and quiescence. The results of these observations are interpretted in terms of a decreasing mass accretion rate and are shown to be in accord with the overall model presented. Finally the concept of the system equilibrium is discussed and used to determine the magnetic moments of the white dwarfs in each system from their spin periods and X-ray luminosities. The values found are shown to be significantly model dependent. The second part of the thesis concerns a survey of the Galactic plane. Scanning observations are used to produce a map of the medium energy X-ray emission and from this a catalogue of 70 sources is compiled. The source list includes many which were previously unidentified. Comments are made on the nature of the sources detected and on the two diffuse components (the Galactic Ridge and the Galactic Bulge) which were observed. Pointed observations were also made at seven of the previously unidentified sources which were detected in the map. These observations are analysed in an attempt to determine the type of object which is producing the emission, and also to gain some insight into possible origins of the two diffuse emission components.