SpringerLink
Forum Springer Astron. Astrophys.
Forum Whats New Search Orders


Astron. Astrophys. 325, 866-870 (1997)

Previous Section Next Section Title Page Table of Contents

1. Introduction

The discovery of high-energy [FORMULA] -radiation from extragalactic compact objects has motivated many authors to consider the effects of [FORMULA] -ray absorption by [FORMULA] - [FORMULA] pair production, eventually inducing pair cascades. The relevance of [FORMULA] - [FORMULA] pair production to astrophysical systems has first been pointed out by Nikishov (1962). The first investigation of the [FORMULA] - [FORMULA] absorption probability of high-energy photons by different soft photon fields, along with some useful approximations, can be found in Gould & Schréder (1967).

The energy spectrum of injected electrons and positrons due to this process has been studied by several authors (e. g., Bonometto & Rees 1971, Aharonian et al. 1983, Zdziarski & Lightman 1985, Coppi & Blandford 1990). In most astrophysically relevant cases, simple approximations can be used for this purpose, without much loss of accuracy. These usually rely on the high-energy photon having much higher energy than the soft photons and thus dominating the energy input and determining the direction of motion of the center-of-momentum frame of the produced pairs. Bonometto & Rees (1971) used basically the same technique as we do, but restricted their analysis to the case [FORMULA], and did not solve the problem analytically. Two recipes to calculate the full energy-dependence of the injected pairs have been published (Aharonian et al. 1983 and Coppi & Blandford 1990), but here the reader is still left with integrations to be carried out numerically.

It is the purpose of this paper to derive the full energy-spectrum of pairs, injected by [FORMULA] - [FORMULA] pair production, exact to second order QED for the case of isotropic radiation fields. In Sect. 2, we give a short overview of the kinematics which are used in Sect. 3 to calculate the pair injection spectrum. In Sect. 4, we compare our results to well-known approximations and specify the limitations of the various approximations. Our analysis is easily generalized to non-isotropic radiation fields. The derivation presented here is widely analogous to the derivation of the pair annihilation spectrum, given by Svensson (1982).

Previous Section Next Section Title Page Table of Contents

© European Southern Observatory (ESO) 1997

Online publication: April 28, 1998

helpdesk.link@springer.de