A Survey of 56 Midlatitude EGRET Error Boxes for Radio Pulsars

We have conducted a radio pulsar survey of 56 unidentified -ray sources from the third EGRET catalog that are at intermediate Galactic latitudes (5 < jbj < 73). For each source, four interleaved 35minute pointings weremadewith the 13 beam, 1400MHzmultibeam receiver on the Parkes 64m radio telescope. This covered the 95 % error box of each source at a limiting sensitivity of 0.2 mJy to pulsed radio emission for periods P k 10 ms and dispersion measures P50 pc cm3. Roughly half of the unidentified -ray sources at jbj> 5 with no proposed active galactic nucleus counterpart were covered in this survey. We detected nine isolated pulsars and four recycled binary pulsars, with three from each class being new discoveries. Timing observations suggest that only one of the pulsars has a spin-down luminosity that is even marginally consistent with the inferred luminosity of its coincident EGRET source. Our results suggest that population models, which include the Gould Belt as a component, overestimate the number of isolated pulsars among the midlatitude Galactic -ray sources, and that it is unlikely that Gould Belt pulsars make up the majority of these sources. However, the possibility of steep pulsar radio spectra and the confusion of terrestrial radio interferencewith long-period pulsars (P k 200ms) having very low dispersionmeasures (P10 pc cm3, expected for sources at a distance of less than about 1 kpc) prevent us from strongly ruling out this hypothesis. Our results also do not support the hypothesis that millisecond pulsars make up the majority of these sources. Nonpulsar source classes should therefore be further investigated as possible counterparts to the unidentified EGRET sources at intermediate Galactic latitudes. Subject headinggs: gamma rays: observations — pulsars: general Online material: color figures