VERY-HIGH-ENERGY GAMMA-RAYS FROM ISOLATED RADIO PULSARS - A SURVEY

During the period 1985-1989 a group of 18 isolated radio pulsars (IRPs) was observed with the Nooitgedacht TeV gamma-ray telescope. These pulsars were selected from a priority list which was compiled by taking both the astrophysical and observational constraints for their observation into account. All IRPs were analyzed in the same way. Of the 18 IRPs observed only one (PSR 1509-58) gave a positive signal over an extended period (1985-1988). No evidence for pulsed emission was seen during the period between 1989 and 1991, however. Two other IRPs (PSR 1823-13 and PSR 1821-24) gave interesting results which merit further observations. These three IRPs are among those having the best chance of being detected (i.e., pulsars with the largest values of E/d2) and all three coincide with possible COS B point sources. Upper limits to the conversion efficiencies of spin-down power to TeV gamma-rays (etagamma) for steady pulsed emission for 17 of the IRPs were compared with the conversion efficiencies predicted from the outer magnetospheric pp model. This comparison indicated that post-Vela-like pulsars are not such good TeV (and hence also MeV to GeV) gamma-ray candidates, as predicted by the outer gap model.