THE PULSAR CONTRIBUTION TO THE DIFFUSE GALACTIC GAMMA-RAY EMISSION

There is active interest in the extent to which unresolved gamma-ray p ulsars contribute to the Galactic diffuse emission, and in whether unr esolved gamma-ray pulsars could be responsible for the excess of diffu se Galactic emission above 1 GeV that has been observed by EGRET. The diffuse gamma-ray intensity due to unresolved pulsars is directly link ed to the number of objects that should be observed in the EGRET data. We can therefore use our knowledge of the unidentified EGRET sources to constrain model parameters like the pulsar birthrate and their beam ing angle. This analysis is based only on the properties of the six pu lsars that have been identified in the EGRET data and is independent o f choice of a pulsar emission model. We find that pulsars contribute v ery little to the diffuse emission at lower energies, whereas above 1 GeV they can account for 18% of the observed intensity in selected reg ions for a reasonable number of directly observable gamma-ray pulsars (similar to 14). The latitude distribution of the diffuse emission cau sed by unresolved pulsars is narrower than that of the observed diffus e emission. While the excess above 1 GeV gamma-ray energy is observed up to at least 6 degrees-8 degrees off the plane, the pulsar contribut ion would be small there. Thus, pulsars do significantly contribute to the diffuse Galactic gamma-ray emission above 1 GeV, but they cannot be made responsible for all the discrepancies between observed intensi ty and model predictions in this energy range.