E. N. Ercan
A study of Galactic bulge X-ray sources with Ariel-5, Exp. C and Ariel-6
1983 (supervisor: A. M. Cruise)

This thesis presents a systematic study of X-ray spectra of galactic bulge X-ray sources. Eight galactic bulge sources were observed by the Experiment-C on Ariel-5 discontinuously over the period February 1975-April 1978. The spectra of six of these sources X1636-53, X1642-45, X1702-36, X1735-44, X1758-20 and X1837+04 are reasonably well fitted by single thermal bremsstrahlung or power law models. The best fit temperatures and hydrogen column densities obtained from a thermal bremsstrahlung model for these sources range between 4-9.5 keV and 5x10^23 H cm^-2. The best fit spectral indices and hydrogen column densities obtained from a power law model range between 2-4 and 1x10^21-1x10^23 H cm^-2, respectively. For X1813-14 and X1728-16 however, no single spectral model yields an acceptable fit to the Ariel-5, Exp. C data. The former reveals a spectral feature between 3 and 4 keV in its thermal continuum. The latter shows a high energy cut-off in the spectrum above 10 keV, suggesting that Comptonization may be important in its formation.

The sources; X1702-36, X1642-45, and X1636-53 are found to be the most active sources in the sample.

With the MSSL/Birmingham University soft X-ray experiment on the Ariel-6 satellite, however, only two sources from this category have been observed: X1728-16, a bright galactic bulge source and X1820-303, a burster and a globular cluster X-ray source, discontinuously over the period April-July, 1980. The soft X-ray spectra of both of these sources are reasonably well fitted by a single power law model.

The results obtained for each source are collected together and compared with the current theoretical models.