STATISTICAL-ANALYSIS OF GAMMA-RAY PROPERTIES OF ROTATION-POWERED PULSARS

Monte Carlo methods are used to simulate the properties of the Galacti c population of rotation-powered pulsars in a model where the gamma ra ys are produced by energetic electrons that Compton-scatter photons ne ar the pulsar polar cap. We use results of radio pulsar statistical st udies to assign the initial magnetic field, spatial, and velocity dist ributions of neutron stars at birth. Gamma-ray and radio fluxes are ca lculated for an observer at Earth and are used to determine the expect ed number of detectable gamma-ray pulsars. The results are compared wi th the observed properties of the seven known gamma-ray pulsars. We in vestigate models where the polar-cap angle is 1, 2, and 4 times larger than the nominal polar-cap angle determined by the open held lines of an aligned dipole magnetic field and where the initial rotation perio d is 20 or 30 ms. We find that the distance, period, age, magnetic fie ld, and gamma-ray flux distributions of the observed gamma-ray pulsars are best represented by a model where the initial pulse period is 30 ms and the polar cap angle is 4 times larger than the nominal angle. F or this model, we predict greater than or similar to 2-4 radio-quiet p ulsars that emit gamma rays at flux levels of the known gamma-ray puls ars. The emission of unresolved gamma-ray pulsars is found to contribu te to the diffuse Galactic gamma-ray continuum at the 5%-10% level.