EDP Sciences
Free access
Volume 429, Number 2, January II 2005
Page(s) 489 - 495
Section Galactic structure, stellar clusters and populations
DOI http://dx.doi.org/10.1051/0004-6361:20041385

A&A 429, 489-495 (2005)
DOI: 10.1051/0004-6361:20041385

Gamma-ray luminosity properties of gamma-ray pulsars

L. Zhang1, 2, Z. X. Han2 and Z. J. Jiang2

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 )

Based on a new self-consistent outer gap model, we statistically study luminosity properties of  $\gamma$-ray pulsars with ages of  $\le$ $2\times 10^7$ yr in the Galaxy as well as those with ages of  $\le$ $5\times 10^6$ yr in the Gould belt using a Monte Carlo method, where the  $\gamma$-ray beaming effect has been included. Generally, the relation between  $\gamma$-ray luminosity,  $L_{\gamma}$, and pulsar spin-down power,  $L_{\rm sd}$, can be expressed as  $L_{\gamma} \propto L^{\delta}_{\rm sd}$, where $\delta$ is a parameter that depends on the galactic latitude and the  $\gamma$-ray threshold. For a given  $\gamma$-ray threshold (for example, the EGRET threshold or GLAST threshold), the parameter  $\delta$ is an increasing function of the galactic latitude. For the EGRET threshold,  $\delta$ changes smoothly with the galactic latitude. For the GLAST threshold, however,  $\delta$ has a minimum at  $\vert b\vert\le 5^{\circ}$, and  $\delta$ increases by a factor of ~ 2 at the range of  $\vert b \vert=
5^{\circ}{-}10^{\circ}$ relative to  $\delta$ at  $\vert b\vert\le 5^{\circ}$ , and then increases smoothly as the galactic latitude further increases. The reason for this is that high galactic latitude  $\gamma$-ray pulsars are dominated by mature pulsars. In fact, the ratio of  $\gamma$-ray pulsars with their ages of  > 106 yr to all simulated  $\gamma$-ray pulsars also increases with the galactic latitude. For the  $\gamma$-ray pulsars produced in a fixed range of galactic latitude, the parameter  $\delta$ increases slightly with the sensitivity of  $\gamma$-ray detector.

Key words: gamma-rays: theory -- stars: pulsars: general -- stars: neutron -- stars: statistics

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