DIFFUSE GAMMA-RAY EMISSION FROM PULSARS IN THE LARGE MAGELLANIC CLOUD

We investigate the contribution of pulsars to the diffuse gamma-ray emission from the Large Magellanic Cloud (LMC). The pulsar birth rate in the LMC is a factor of approximately 10 lower than that of the Galaxy and the distance to pulsars in the LMC is approximately 5-10 times larger than to Galactic pulsars. The resulting total integrated photon flux from LMC pulsars is thus reduced by a factor approximately 10(2-3). However, the surface brightness is not reduced by the same amount because of the much smaller angular extent of the LMC in comparison to the diffuse glow from the Galactic plane. We show that gamma-ray emission due to pulsars born in the LMC could produce gamma-ray fluxes that are larger than the inverse Compton component from relativistic cosmic-ray electrons and a significant fraction of the extragalactic isotropic background or the diffuse Galactic background in that direction. The diffuse pulsar glow above 100 MeV should therefore be included in models of high-energy emission from the LMC. For a gamma-ray beaming fraction of order unity the detected emissions from the LMC constrain the pulsar birth rate to less than one per 50 yr. This limit is about one order of magnitude above the Supernova rate inferred from the historic record or from the star-formation rate.