Implications of the Cosmic Ray Electron Spectrum and Anisotropy measured with Fermi-LAT

TL;DR

This paper analyzes Fermi-LAT data on cosmic ray electrons, confirming two spectral components, validating propagation models, and suggesting nearby pulsars as sources consistent with anisotropy constraints.

Contribution

It provides new measurements extending the CRE spectrum down to 7 GeV, supports a two-component spectral model, and evaluates source candidates and propagation models against observational constraints.

Findings

Two distinct electron and positron spectral components are supported.

Propagation models with Kraichnan and plain-diffusion are validated, Kolmogorov is disfavored.

Nearby pulsars are consistent sources with anisotropy constraints.

Abstract

The Fermi Large Area Telescope (LAT) collaboration recently released the updated results of the measurement of the cosmic ray electron (CRE) spectrum and published its first constraints on the CRE anisotropy. With respect to the previous Fermi-LAT results, the CRE spectrum measurement was extended down from 20 to 7 GeV, thus providing a better lever arm to discriminate theoretical models. Here we show that the new data strengthen the evidence for the presence of two distinct electron and positron spectral components. Furthermore, we show that under such hypothesis most relevant CRE and positron data sets are remarkably well reproduced. Consistent fits of cosmic-ray nuclei and antiproton data, which are crucial to validate the adopted propagation setup(s) and to fix the solar modulation potential, are obtained for the Kraichnan and plain-diffusion propagation setups, while the Kolmogorov one is disfavored. We then confirm that nearby pulsars are viable source candidates of the required $e^\pm$ extra-component. In that case, we show that the predicted CRE anisotropy is compatible with Fermi-LAT constraints and that a positive detection should be at hand of that observatory. Models assuming that only nearby supernova remnants contribute to the high energy tail of the observed CRE spectrum are in contrast with anisotropy limits.