Gamma‐Ray Emission Properties from Mature Pulsars in the Galaxy and in the Gould Belt

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Abstract
We study the γ-ray emission properties of pulsars by using a new self-consistent outer gap model. The outer gap can exist in pulsars older than 1 million yr if the effect of magnetic inclination angle, as well as the average properties of the outer gap, are considered. The mature γ-ray pulsars, whose ages are between 0.3 and 3 million yr, are able to move up to high Galactic latitude. Moreover, their γ-ray luminosities are weaker, and their spectra are significantly softer than those of younger γ-ray pulsars in the Galactic plane. We use a Monte Carlo method to simulate the statistical properties of γ-ray pulsars in the Galaxy as well as in the Gould Belt. We find that γ-ray pulsars located at b < 5° and b > 5° have very different properties. High Galactic latitude γ-ray pulsars are dominated by mature pulsars with longer periods, weaker fluxes, and softer spectra. If the pulsar birth rates in the Galaxy and the Gould Belt are ~10-2 and ~2 × 10-5 yr-1, respectively, there are 42 and 35 radio-quiet γ-ray pulsars for b < 5° and b > 5°, respectively. The number of radio-quiet γ-ray pulsars from the Gould Belt are 2 and 13 for b < 5° and b > 5°, respectively. We suggest that a good fraction of unidentified EGRET γ-ray sources may be these radio-quiet γ-ray pulsars. Furthermore, γ-ray pulsars located at b > 5° satisfy Lγ ∝ L, whereas Lγ ∝ L for γ-ray pulsars in the Galactic plane, where β ~ 0.6 and δ ~ 0.3, respectively.
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