Vol 11, No 7 (2011) / Wang

Possible distance indicators in gamma-ray pulsars

Wei Wang

Abstract

Distance measurement of gamma-ray pulsars is a current challenge in pulsar studies. The Large Area Telescope (LAT) aboard the Fermi gamma-ray observatory discovered more than 70 gamma-ray pulsars including 24 new gamma-selected pulsars with almost no distance information. We study the relation between gamma-ray emission efficiency (η = Lγ /Edot) and pulsar parameters for young radio-selected gamma-ray pulsars with known distance information in the first gamma-ray pulsar catalog reported by Fermi/LAT. We have introduced three generation-order parameters to describe the gamma-ray emission properties of pulsars, and find a strong correlation of η−ζ3 , a generation-order parameter which reflects γ-ray photon generation in the pair cascade processes induced by magnetic field absorption in a pulsar’s magnetosphere. A good correlation of ηBLC , the magnetic field at the light cylinder radius, is also found. These correlations are the distance indicators in gamma-ray pulsars used to evaluate distances for gamma-selected pulsars. Distances of 25 gamma-selected pulsars are estimated, which could be tested by other distance measurement methods. The physical origin of the correlations may also be interesting for pulsar studies.

Keywords


gamma rays: general — pulsars: general — stars: neutron

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