A study of the background and of diffuse and extended XUV emission in the ROSAT Wide-Field Camera all-sky survey.

This thesis presents the results of a study of the characteristics and the origins of the background components in the ROSAT Wide-Field Camera. Contributions from six distinct sources have been positively identified: 1) cosmic rays and other high-energy (E ~ 1 MeV) charged particles, 2) low-energy (E ~ 50keV) electrons in the auroral zones, 3) a spacecraft glow phenomenon, similar to that observed on the Space Shuttle, but confined to the far-ultraviolet regime, 4) resonantly scattered Solar EUV line photons, for example He II 304A, 5) a charged particle component from an unidentified source (possible ring current precipitation), and 6) intrinsic noise in the WFC microchannel plate detectors. In addition, the results of a search for positively idenfitiable signatures from the diffuse XUV background are presented. No features have been identified in the background, which places a strong upper limit on the diffuse flux which is nearly an order of magnitude lower than that implied from previous surveys in this waveband. This finding has serious implications for the displacement model of the local interstellar medium. An analysis of the WFC images of the Vela and Cygnus Loop supernova remnants is also presented. The WFC survey data from the Vela SNR are combined with data taken with the ROSAT PSPC in a spatially resolved joint spectral fitting effort, work which is made possible only by the quality of the PSPC data. The results show for the first time that two gas phases are present at distinct temperatures with differing spatial distributions, and that the variations in the X-ray temperature across the remnant inferred in previous (single temperature) analyses are probably due to changes in the emission measure ratio of the two components.