The Local Interstellar Spectrum of Cosmic Ray Electrons

Abstract

The direct measurements of electrons and positrons over the last 30 years, corrected for the solar effect in the force-field approximation, are considered. The resulting overall electron spectrum may be fitted with a single power law above few GeV with spectral index (${\gamma }_{-}=3.41\pm 0.02$), consistent with the spectral index of the positron spectrum (${\gamma }_{+}=3.40\pm 0.06$), therefore suggesting a common acceleration process for both species. We propose that the engine was a shock wave originating from the last supernova explosion among those that formed the local bubble. In addition, at low energy, the electron spectrum measured during the last $A+$ solar phase is damped, whereas the positron spectrum is well represented by a single power law down to the lowest inferred local interstellar energy (0.8 GeV). We suggest that this difference arises from a time- and charge-dependent effect of the solar modulation that is not taken into account by the force-field approximation.

10 pages, 9 figures, 1 table. OBSOLETE: please refer to ApJ 612 (2004) 262-267, that is the final version of this work

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