Cosmic-ray electrons and positrons

Measurements of cosmic-ray electrons and positrons address a number of significant astrophysical questions concerning the nature and distribution of sources in the galaxy, and the characteristics of cosmic ray propagation in the galactic disk and halo. The abundance of positrons may also carry the signature of tn unusual pair production processes or dark matter particle decays. We shall review the body of information available, including recent results from the HEAT collaboration. We describe constraints on the source energy spectrum of electrons, which appears to have the same shape as that of nuclear cosmic rays, and we discuss the evidence that positrons are predominantly if not exclusively of interstellar secondary origin. Finally, we emphasize the need for several key observations that are required in the future in order to resolve the remaining questions. (C) 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.