Introduction

In Chapter 18, we showed that we can make a convincing case that the high energy electrons which are observed at the top of the atmosphere represent a sample of the high energy electrons present throughout the interstellar medium and which are responsible for the diffuse Galactic synchrotron radio emission. Our task in this chapter is to interpret these observations in terms of the propagation of these particles from their sources through the interstellar medium and the energetics of possible energy sources within the Galaxy. The key diagnostic tools are aging processes, which can result in features in the energy spectra of the electrons and estimates of the energy requirements of sources of synchrotron radiation. In this chapter, we will develop these tools in the context of the origin of the Galactic radio emission and the study of supernovae as sources of high energy electrons. These tools are, however, of very general applicability to the whole of high energy astrophysics. We will use them repeatedly in our discussion of the physics of radio sources and active galactic nuclei.

Energy loss processes for high energy electrons

High energy electrons are subject to a number of energy loss processes as they propagate from their sources through the interstellar medium. The loss processes cause distortions of the injection energy spectra of the particles from their sources and thus potentially provide information about the life histories of the high energy electrons.