ON THE CORRELATION BETWEEN PROPER-MOTION VELOCITIES AND SCINTILLATIONVELOCITIES 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 sp eeds are systematically lower than those from interferometric measurem ents by factors of 2 or so. The subsequent improvement of the pulsar d istance scale and the recent revision of the scintillation velocity fo rmula significantly influence this comparison A new comparison of prop er motion and scintillation speeds for 59 pulsars is presented here. T he two speeds are found to agree quite well, and there is no systemati c bias. For some pulsars the difference between the two speeds is foun d to be more than expected from the typical estimation errors alone. F or pulsars with large z-heights, this discrepancy is found to be consi stent with a 1 kpc scare height for the scattering material in the loc al Galactic neighborhood. For many of the low z-height pulsars showing a discrepancy between the two speeds, enhanced scattering from the lo cal Orion arm of the Galaxy is found to be a suitable explanation.