ON THE CORRELATION BETWEEN PROPER-MOTION VELOCITIES AND SCINTILLATION VELOCITIES OF RADIO PULSARS

A comparison of pulsar transverse speeds measured using the techniques of (1) interferometric measurements of angular proper motion and (2) motion of the pattern of interstellar scintillations shows significant correlation. However, recent studies have found that scintillation speeds are systematically lower than those from interferometric measurements by factors of 2 or so. The subsequent improvement of the pulsar distance scale and the recent revision of the scintillation velocity formula significantly influence this comparison A new comparison of proper motion and scintillation speeds for 59 pulsars is presented here. The two speeds are found to agree quite well, and there is no systematic bias. For some pulsars the difference between the two speeds is found to be more than expected from the typical estimation errors alone. For pulsars with large z-heights, this discrepancy is found to be consistent with a 1 kpc scare height for the scattering material in the local Galactic neighborhood. For many of the low z-height pulsars showing a discrepancy between the two speeds, enhanced scattering from the local Orion arm of the Galaxy is found to be a suitable explanation.