The problem

We have left to the last chapter of this volume one of the most intriguing problems in high energy astrophysics – the mechanisms by which high energy particles are accelerated to ultrarelativistic energies. In these first two volumes, sites where particles are accelerated include solar flares, the boundary of the Earth's magnetosphere, pulsar magnetospheres, supernovae and supernova remnants. In volume 3, we will find evidence for particle acceleration in active galactic nuclei and in extended radio sources. It is appropriate to consider the problem of the acceleration of charged particles at this point because a number of important features of the cosmic rays are common to the energy spectra of particles in other astrophysical environments.

The specific features of particle acceleration which we have to account for are as follows.

1. 1 A power-law energy spectrum for particles of all types. The energy spectrum of cosmic rays and the electron energy spectrum of many non-thermal sources have the form

2. where the exponent x lies in the range roughly 2.2–3. For the cosmic rays, x = 2.5–2.7 at energies ∼ 1–103 GeV (Section 9.1), with slightly flatter spectra for primary nuclei such as iron. The typical spectra of radio sources correspond to electron spectra with x ≈ 2.6 with a scatter of about 0.4 about this mean value. The continuum spectra of quasars in the optical and X-ray wavebands correspond to x ∼ 3.

3. 2 The acceleration of cosmic rays to energies E ∼ 1020 eV.

4. 3 […]