Shock-associated plasma density fluctuations in the interstellaer medium

Theories of diffusive shock acceleration of the cosmic rays predict that there should be regions of intense Alfven waves both upstream and downstream of the shock front. Observations of similar waves near solar system shock waves show that they produce substantial density fluctuations. Such density fluctuations might produce observable scattering of radio waves. We discuss observations which have searched for angular broadening of 'blurring' of radio sources whose lines of sight pass close to or through supernova remnants. No definite cases of remnant-associated scattering have been detected. However, the source CL4, which is viewed through the Cygnus Loop supernova remnant, may be such an object and merits further observation. (author). 5 refs.; 3 figs