Gamma-ray Emission Properties from Mature Pulsars in the Galaxy and in the Gould Belt

Abstract

We study the $\gamma$-ray emission properties of pulsars by using a new self-consistent outer gap model. The outer gap can exist in pulsars with age over million years old if the effect of magnetic inclination angle as well as the average properties of the outer gap are considered. The mature $\gamma$-ray pulsars, whose ages are between 0.3 to 3 million years old, are able to move up to high galactic latitude. Moreover, their $\gamma$-ray luminosity are weaker and their spectra are softer than those of younger $\gamma$-ray pulsars in the galactic plane significantly. We use a Monte Carlo method to simulate the statistical properties of $\gamma$-ray pulsars in the Galaxy as well as in the Gould Belt. We find that $\gamma$-ray pulsars located at $\mid b\mid <5^{\circ }$ and located at $\mid b\mid >5^{\circ }$ have very different properties. High galactic latitude $\gamma$-ray pulsars are dominated by mature pulsars with longer periods, weaker fluxes and softer spectra. If the pulsar birth rate in the Galaxy and the Gould Belt are $\sim 10^{-2}y{r}^{-1}$ and $\sim 2\times 10^{-5}y{r}^{-1}$ respectively, there are 42 and 35 radio-quiet $\gamma$-ray pulsars for $\mid b\mid <5^{\circ }$ and $\mid b\mid >5^{\circ }$ respectively. Radio-quiet $\gamma$-ray pulsars from the Gould Belt are 2 and 13 for $\mid b\mid <5^{\circ }$ and $\mid b\mid >5^{\circ }$ respectively. We suggest that a good fraction of unidentified EGRET $\gamma$-ray sources may be these radio-quiet $\gamma$-ray pulsars. Furthermore $\gamma$-ray pulsars located at $\mid b\mid >5^{\circ }$ satisfies $L_{\gamma }\propto L_{sd}^{\beta }$ whereas $L_{\gamma }\propto L_{sd}^{\delta }$ for $\gamma$-ray pulsars in the galactic plane, where $\beta \sim 0.6$ and $\delta \sim 0.3$ respectively.

arXiv comment24 pages, 21 figures, accepted to be published in ApJ

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• A Survey of 56 Mid-latitude EGRET Error Boxes for Radio Pulsars
• Source population synthesis and the Galactic diffuse gamma-ray emission
• Contribution to diffuse gamma-rays in the Galactic center region from unresolved millisecond pulsars
• Population study for gamma-ray pulsars with the outer gap model
• Transient X-ray Emission from Normal Galactic Nuclei
• Possible TeV Source Candidates In The Unidentified EGRET Sources
• Pulsars and Their Nebulae as EGRET Sources
• Searching for Radio Pulsars in 3EG Sources at Urumqi Observatory