Gamma‐Ray Emission from Rotation‐powered Pulsars

Abstract

Using a simplified model of cascade pair creation over pulsar polar caps, presented in two previous papers, we investigate the expected γ-ray output from pulsars' low-altitude particle acceleration and pair creation regions. We divide pulsars into several categories, based on which mechanism truncates the particle acceleration off the polar cap, and give estimates for the expected luminosity of each category. We find that inverse Compton scattering above the pulsar polar cap provides the primary γ-rays that initiate the pair cascades in most pulsars. This reduces the expected γ-ray luminosity below previous estimates, which assumed that curvature γ-ray emission was the dominant initiator of pair creation in all pulsars. Even for the brightest pulsars, where curvature radiation sets the height of the pair formation front, we find predicted luminosities too low to explain the EGRET pulsars, suggesting that the source of that emission is an outer magnetosphere accelerator. The predicted polar cap luminosities are high enough, however, to be observable by upcoming γ-ray instruments, providing a firm test for this theory.