Scattering of pulsar radiation and electron density turbulence in the interstellar medium

We report measurements, using the Culgoora circular array at 80 and 160 MHz and the Parkes 64 m telescope at 410 MHz, of the pulse broadening due to interstellar scattering on 33 pulsars. These results are added to published data on 52 other pulsars in order to investigate the interstellar turbulence levels over 85 paths in the Galaxy. We find a significant relation between the turbulence level C~ and dispersion measure, heliocentric distance, galactocentric distance, galactic latitude and galactic longitude. Our results are consistent with a distribution of turbulence that peaks near the galactic centre and extends out to past the solar circle, with the scale height perpendicular to the plane at least equal to that of the pulsars. The magnitude of the fluctuations in electron density responsible for the scattering is not proportional to the average electron density, but increases much more rapidly than the latter as the galactic centre is approached. The apparent dependence of C~ on heliocentric distance is preferentially interpreted as due to the presence of a highly clumped distribution of turbulence along all lines of sight.