The gamma-ray pulsar population

We apply a likelihood analysis to pulsar detections, pulsar upper limits, a nd diffuse background measurements from the OSSE and EGRET instruments on t he Compton Gamma Ray Observatory to constrain the luminosity law for gamma- ray pulsars and some properties of the gamma-ray pulsar population. We find that the dependence of luminosity on spin period and dipole magnetic field is much steeper at OSSE than at EGRET energies (50-200 keV and >100 MeV, r espectively), suggesting that different emission mechanisms are responsible for low- and high-energy gamma-ray emission. Incorporating a spin-down mod el and assuming a pulsar spatial distribution, we estimate the fraction of the Galactic gamma-ray background due to unidentified pulsars and find that pulsars may be an important component of the OSSE diffuse flux but are mos t likely not important at EGRET energies. Using measurements of the diffuse background flux from these instruments, we are able to place constraints o n the braking index, initial spin period, and magnetic field of the Galacti c pulsar population and are also able to constrain the pulsar birthrate to be between 1/25 yr(-1) and 1/500 yr(-1). Our results are based on a large g amma-ray beam, but they do not scale in a simple way with beam size. We est imate that about 20 of the 169 unidentified EGRET sources are probably gamm a-ray pulsars. We use our model to predict the pulsar population that will be seen by future gamma-ray instruments and estimate that Gamma Ray Large A rea Space Telescope will detect roughly 750 gamma-ray pulsars as steady sou rces, only 120 of which are currently known radio pulsars.