Gamma-Ray Pulsars: Beaming Evolution, Stats and Unident. EGRET Sources
  We compute the variation of the beaming fraction with the efficiency of high energy gamma-ray production in the outer gap pulsar model of Romani and Yadigaroglu. This allows us to correct the fluxes observed for pulsars in the EGRET band and to derive a simple estimate of the variation of efficiency with age. Integration of this model over the population of young neutron stars gives the expected number of gamma-ray pulsars along with their distributions in age and distance. This model also shows that many of the unidentified EGRET plane sources should be pulsars, and predicts the gamma-ray fluxes of known radio pulsars. The contribution of unresolved pulsars to the background flux in the EGRET band is found to be about 5 %. For an animation of our pulsar model see http://geminga.stanford.edu/users/ion/home.html . 
I.-A. Yadigaroglu and Roger W. Romani