UPPER LIMITS ON THE HIGH-ENERGY GAMMA-RAY FLUXES FROM PSR-1951-58(32 AND 1509)

The high-energy gamma-ray telescope EGRET observed the positions of tw o young pulsars, PSR 1951 + 32 and 1509 - 58, during its all-sky surve y. Despite their youth and relative proximity to the Earth, neither pu lsar is detected as a point source or in periodicity analysis. Flux li mits of a few x 10(-7) photon cm-2 s-1 are obtained for emission above 100 MeV, and approximately 10(-6) photon cm-2 s-1 for 30-100 MeV. For the conventional assumption of beaming into 1 sr, the flux limits sug gest that less than 3.2 per cent of the radiation from PSR 1509-58, an d less than 1.8 per cent from PSR 1951 + 32, is in the form of beamed high-energy gamma-rays. The PSR 1509 - 58 limits lie approximately one order of magnitude below the extrapolated hard X-ray spectrum and sug gest that the spectrum steepens in the MeV region.