Gamma-Ray Evidence for Cosmic-Ray Sources.

Available from UMI in association with The British Library. Requires signed TDF. The origin of cosmic-rays is one of the long-standing problems in astrophysics. In recent years, strong evidence has been found that certain classes of object contain and are able to accelerate particles to high energies. In this thesis the origin problem is addressed in two different ways. Firstly, two different regions of the Galaxy are studied using gamma-ray observations from the COSB satellite combined with atomic and molecular gas measurements. The Vela region contains a pulsar and a supernova remnant and is particularly valuable location for cosmic-ray studies because of its proximity, the association of the two objects, and the intensity of the gamma -ray flux it produces. At greater longitudes, the region around the peculiar object eta Carinae is also studied. It is rich in potential sources of cosmic rays including active stars and a spiral arm seen at a tangent at l ~ 282^circ . Analysis of the Vela region reveals strong evidence for cosmic ray production at all energies observed by COSB. The supernova remnant seems the most likely candidate, but the possibility of the pulsar itself producing some of the particles cannot be ruled out. The excess gamma-ray emission from around eta Carinae does not appear correlated with the active stars but seems to be coming predominantly from the spiral arm. This is the first time evidence has been presented for cosmic-ray acceleration by the spiral shock in a particular, known spiral arm which is observed as a feature in the gas. The gamma-rays are produced in the gas clouds associated with this arm. The second approach to the cosmic-ray origin problem involves a model for cosmic-ray production in supernova remnants and is used in association with a Monte-Carlo simulation of their occurrence in the Galaxy. Unlike earlier models (Bhat et al. 1987), the motion of the Sun is also taken into account and the supernova explosions occur mainly in spiral arms. The results are in the form of a time sequence of energy density values and are compared in detail with ¹⁰Be results. It is found that the model accounts for the long-term rise in the concentration of this radioisotope and does not predict large excursions from the mean energy density that beset older models. Thus the cosmic ray production by supernova remnants seems to be consistent with the radioisotope data.