Very high energy gamma rays from millisecond pulsars

Abstract

In this paper we concentrate on the emission of TeV γ - rays from radio pulsars. It will be shown that the polar gap model fails to explain the observed TeV flux levels: The X-ray luminosity should exceed the TeV luminosity if the latter originates from the polar gap regions. The outer gap model of Cheng, Ho and Ruderman provides a consistent picture of TeV γ - ray emission: The total gap power is converted to TeV γ - rays by means of the inverse Compton scattering of primary electrons on the abundant soft IR flux in and around the gap. A fraction exp(-f- 1 2) escapes photon-photon absorption and may be observable Here f (∼ 0.1 for Vela and Vela-like pulsars) is the fraction of the open magnetosphere occupied by the gap. The remaining power is used for the gap sustaining mechanism. As the pulsar grows older, f → 1 and the TeV power increases and becomes comparable to the spindown power. This is the so-called "post Vela-like" stage. The model is applied to millisecond pulsars which are all Vela- and post Vela-like. The luminosity estimates are consistent with the TeV observations - despite the experimental uncertainties and theoretical assumptions. © 1990.