Gamma-ray luminosity properties of gamma-ray pulsars

¹ National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, PO Box 110, Kunming, PRC, PR China e-mail: astroynu@public.km.yn.cn
² Department of Physics, Yunnan University, Kunming, PR China

Received: 2 June 2004
Accepted: 30 August 2004

Abstract

Based on a new self-consistent outer gap model, we statistically study luminosity properties of γ-ray pulsars with ages of ≤ yr in the Galaxy as well as those with ages of ≤ yr in the Gould belt using a Monte Carlo method, where the γ-ray beaming effect has been included. Generally, the relation between γ-ray luminosity, , and pulsar spin-down power, L_sd, can be expressed as , where δ is a parameter that depends on the galactic latitude and the γ-ray threshold. For a given γ-ray threshold (for example, the EGRET threshold or GLAST threshold), the parameter δ is an increasing function of the galactic latitude. For the EGRET threshold, δ changes smoothly with the galactic latitude. For the GLAST threshold, however, δ has a minimum at , and δ increases by a factor of ~2 at the range of  relative to δ at , and then increases smoothly as the galactic latitude further increases. The reason for this is that high galactic latitude γ-ray pulsars are dominated by mature pulsars. In fact, the ratio of γ-ray pulsars with their ages of >10⁶ yr to all simulated γ-ray pulsars also increases with the galactic latitude. For the γ-ray pulsars produced in a fixed range of galactic latitude, the parameter δ increases slightly with the sensitivity of γ-ray detector.