ANGULAR BROADENING OF PULSARS AND THE DISTRIBUTION OF INTERSTELLAR PLASMA FLUCTUATIONS

Comparison of angular and temporal broadening for 10 pulsars suggests a uniform distribution of scattering material in the interstellar plasma with localized, strong scattering near young supernova remnants. Angular broadening and temporal broadening both measure the integrated strength of scattering along the line of sight, but with different weighting functions. Comparison of the two thus yields information on the distribution of scattering material along the line of sight. We report new measurements of angular diameter for the scattering disks of eight pulsars, and discuss two measurements from the literature. We compare these results with published measurements of temporal broadening. Scattering disks of four pulsars are unresolved, but are close to the speckle regime of interstellar scattering. Four of the objects show moderate scattering. In the context of a model consisting of a thin screen superposed on a uniform medium, comparison of angular and temporal broadening suggests that the localized component of scattering has strength approximately 3 times that of the uniform medium. Signals from the Crab (0531 + 21) and Vela (0833 - 45) pulsars are heavily scattered by their surrounding supernova remnants; scattering by the remnants is more than 38 times as strong as by the uniform medium. The fluctuations responsible for this scattering may be associated with cosmic-ray acceleration. We compare strengths and spatial spectra of the scattering material in the supernova remnants that enclose these pulsars, and in the supernova remnant CTB 80, which encloses pulsar 1951 + 32. Remnants show significant differences in scattering properties.