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Session 53 - Gamma Ray Investigations.
Oral session, Thursday, June 12
North Main Hall F/G,
This dissertaion talk concerns a VLA study of nearby spiral galaxies and the identification of SNRs and HII regions within these galaxies. The origin of cosmic rays remains a mystery even after decades of research. We present unique empirical evidence that Type II supernovae are the precursors of cosmic-ray producing supernova remnants. This evidence is based on VLA observations of NGC 6946, a large, nearby, spiral galaxy. From a sample of 64 supernova remnants, 39 exhibited nonthermal radio emission. The supernova remnants without radio emission are located in the inter-arm regions, whereas the supernova remnants with radio emission are located on the spiral arms. The spiral arms are sites of recent star formation, including the massive, short-lived stars that are the progenitors of Type II supernovae. This evidence leads to the conclusion that Type II supernovae result in cosmic-ray producing supernova remnants. This is the first time that the progenitors of cosmic-ray producing supernova remnants have been identified empirically. We discuss models of particle acceleration that predict cosmic ray production and compare the results to our sample of SNRs. This comparison can determine the importance of environment versus initial conditions (i.e. blast energy) ofor quantities of cosmic rays produced.
