IDENTIFICATION OF PSR1758-23 AS A RUNAWAY PULSAR FROM THE SUPERNOVA REMNANT W28

THE discovery1 of the pulsar 1758 - 23 in the vicinity of the radio su pernova remnant W28 has prompted speculation that the two might be phy sically associated. Although the brightening of the supernova remnant in the direction of the pulsar suggests such an association 2, the lar ge column density of electrons in the interstellar medium towards PSR1 758 - 23 (evident from the pronounced dispersion of the radio signal) and the anomalously large scattering observed in the pulses seem to in dicate1,3 a distance much greater than that to W28. Here we present ne w observations which indicate that the large dispersion and scattering of the pulses is instead caused by a dense screen of ionized material located along the line of sight, and thus the distances to the pulsar and W28 can be reconciled. Similar scattering screens have been repor ted previously4,5 and appear to be associated with H II regions; the p roperties of these screens seem, however, to be inconsistent with curr ent models6 of turbulent structure in the interstellar medium.