Gamma-ray emission properties from mature pulsars in the Galaxy and in the Gould Belt

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 L γ α L sd β, whereas L γ α L sd δ for γ-ray pulsars in the Galactic plane, where β ∼ 0.6 and δ ∼ 0.3, respectively.