G. S. G. Pollard
X-ray background studies with Ariel 5 and Copernicus observations of the X-ray source: OAO1653-40
1980 (supervisor: P. W. Sanford)

The MSSL/UCL X-ray proportional counter onboard the Ariel 5 satellite has been used to examine the spectra of the 2 to 20 keV X-ray background in order to search for any line emissions. A review of the history and possible production mechanisms of the X-ray background is presented. In particular a critical analysis of the published data, which have shown there to be a possible break at 20 - 30 keV in the background, is included.

A description of normal (i.e. stellar) data analysis techniques is given with an extension describing modifications which have allowed the analysis of the data so as to extract the X-ray background. Spectra of the 2 - 20 keV background are presented along with upper limits to any line emission. The analysis of these data includes an extensive 'post-launch' spectral calibration of the instrument. In particular, higher energy photon losses in multi-wire proportional counters is described. An examination of the spacecraft's environment is also presented and much discussion is given as to the possible methods of eliminating the contaminating effect that charged particles have on the proportional counter data. Using these methods, attempts have been made to predict charged particle intensities by use of various models involving spacecraft and experiment parameters.

One chapter of this dissertation is devoted to the study of X-ray background spatial intensity fluctuations. A novel method of fluctuations analysis, which uses the experiment C quadrant mode of data collection, is described. Fluctuation limits derived by 'standard' analysis techniques and by this 'quadrant subtraction' technique are given.

The final chapter describes the X-ray data obtained from the Copernicus MSSL/UCL 2.5 - 10 keV proportional counter which have led to the conclusion that the stellar binary system V861 Sco is a variable X-ray source. The combination of this result and the known limits for the mass of the system indicate that the secondary is a compact object and is most probably a black hole. This conclusion is discussed along with the implications of more recent simultaneous Copernicus and HEAO-A X-ray observations.