On possible interpretations of the high energy electron-positron spectrum measured by the Fermi Large Area Telescope

TL;DR

The paper analyzes Fermi-LAT's high-energy electron-positron spectrum measurements, exploring interpretations involving Galactic sources, pulsars, and dark matter, and discusses how combined experimental data challenge single-component models.

Contribution

It evaluates the consistency of different models explaining the CRE spectrum and proposes combined scenarios involving pulsars and dark matter as more plausible explanations.

Findings

Single component models are inconsistent with combined data.

Multiple source scenarios can fit the combined experimental results.

Anisotropy measurements could help distinguish between pulsar and dark matter origins.

Abstract

The Fermi-LAT experiment recently reported high precision measurements of the spectrum of cosmic-ray electrons-plus-positrons (CRE) between 20 GeV and 1 TeV. The spectrum shows no prominent spectral features, and is significantly harder than that inferred from several previous experiments. Here we discuss several interpretations of the Fermi results based either on a single large scale Galactic CRE component or by invoking additional electron-positron primary sources, e.g. nearby pulsars or particle Dark Matter annihilation. We show that while the reported Fermi-LAT data alone can be interpreted in terms of a single component scenario, when combined with other complementary experimental results, specifically the CRE spectrum measured by H.E.S.S. and especially the positron fraction reported by PAMELA between 1 and 100 GeV, that class of models fails to provide a consistent interpretation. Rather, we find that several combinations of parameters, involving both the pulsar and dark matter scenarios, allow a consistent description of those results. We also briefly discuss the possibility of discriminating between the pulsar and dark matter interpretations by looking for a possible anisotropy in the CRE flux.