Acceleration of Cosmic Rays in Supernova Remnants

Abstract

Cosmic rays have been an interesting and challenging problem in astrophysics since their discovery by Victor Hess (1912). The up-to-date information is collected in the proceedings (and references therein) of the biannual International Cosmic Ray Conference, the most recent ones in Bangalore (1983), La Jolla (1985) and Moscow (1987). Furthermore, this introduction is not intended as a balanced review on the field and we will concentrate on certain aspects of the acceleration of cosmic rays in supernova remnants (SNR’s). Therefore we restrict the following discussion on the socalled galactic component of cosmic rays in the range between 1 GeV/nuc and 106 GeV/nuc, where most of the cosmic ray energy is concentrated (e.g. Axford 1981), and in particular to the acceleration of particles in SNR’s. The importance of the acceleration of cosmic rays and their influence on other astrophysical events has been discussed e.g. by Volk (1987). Solar modulation affects significantly the interpretation of the observations for the lower particle energies between 1 GeV and 10 GeV (Parker 1958). Particles with energies as large as 1020 eV/nuc have been detected and this raises the question which process can accelerate single particles to such energies. The cosmic ray energy density is about ec = 1 eV cm−3 (at least in the solar neighbourhood) and since the charged particles are tied to the magnetic field which permeates the interstellar medium, we have an intimate relation between these energetic particles and the other interstellar components. The gyroradius of a high energy proton is given by r g ⋍ E[GeV]/B[μG]pc. Note that this energy density is comparable to that of the magnetic field, the interstellar photon field, the turbulent and ordered motions of the interstellar gas. The interstellar gas is mainly heated by shock waves and this equipartition of energies suggests a connection between shock waves and the acceleration process of particles. According to this energy argument cosmic rays play an important role for the dynamics of the interstellar medium.