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

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.

23 pages, 22 figures. Accepted for publication in Astroparticle Physics. Some of the results presented in this paper have been derived with the DRAGON package which is now public at the website: http://www.desy.de/~maccione/DRAGON/

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• Origin of Cosmic Rays
• A common solution to the cosmic ray anisotropy and gradient problems
• Unveiling the nature of dark matter with high redshift 21 cm line experiments
• The nature of dark matter from the global high redshift HI 21 cm signal
• Low energy cosmic ray positron fraction explained by charge-sign dependent solar modulation
• Solution to the cosmic ray anisotropy problem
• Search for Cosmic-Ray Electron and Positron Anisotropies with Seven Years of Fermi Large Area Telescope Data
• Discriminating the source of high-energy positrons with AMS-02
• A self-consistent model of cosmic-ray fluxes and positron excess: Roles of nearby pulsars and a sub-dominant source population