Cosmic Ray Electrons and Positrons — a Review of Current Measurements and Some Implications

Abstract

We review recent measurements of cosmic ray electrons and positrons. In contrast to the earlier situation there now appears to be good agreement between different measurements of the electron spectrum at 10 GeV. These measurements are consistent with the previous so called “high” intensities. This new level of agreement permits the interstellar electron spectrum to be derived in a more precise way directly from the radio background measurements. This new electron spectrum is interpreted with regard to its implications for the various energy loss processes occurring in interstellar space and also for its implications regarding the production of gamma-rays below ~ 100 MeV. A primary electron spectrum after accleleration with an index of -2.3 ± 0.1 between a few MeV and several hundred GeV is consistent with the data.

All positron measurements can be made consistent if previously measured e⁺(e⁺ + e^- ) ratios are assumed to be correct and all electron intensities are normalized to the “high” electron spectrum as defined by recent measurements. This leads to an interstellar positron intensity ~ 50% higher than previously assumed, requiring a proton path length ~ 10 g/cm².

The distribution of electrons in the galaxy can be appproximated by an effective disk of half thickness ~ 1 Kpc. within this disk the electron spectral shape appears to remain remarkably constant as a function of position. The intensity falls off only slowly from the center out to a distance ~ 12 Kpc, with the intensity within the spiral arms being perhaps a factor ~ 2 higher than that between the arms.