The `excess' of primary cosmic ray electrons

TL;DR

Recent precise measurements of cosmic ray electrons and positrons reveal an unexpected excess of primary electrons at 100-400 GeV, challenging standard models and suggesting nearby supernova remnants as likely sources.

Contribution

This paper identifies a significant excess of primary cosmic ray electrons at high energies, supported by recent AMS-02 data, and proposes nearby supernova remnants as the origin.

Findings

The electron-positron flux difference indicates an excess of primary electrons.

The excess flux at 100-400 GeV is comparable to the positron excess.

Nearby supernova remnants are favored as sources for this excess.

Abstract

With the accurate cosmic ray (CR) electron and positron spectra (denoted as $\Phi_{\rm e^{-}}$ and $\Phi_{\rm e^{+}}$, respectively) measured by AMS-02 collaboration, the difference between the electron and positron fluxes (i.e., $\Delta \Phi=\Phi_{\rm e^{-}}-\Phi_{\rm e^{+}}$), dominated by the propagated primary electrons, can be reliably inferred. In the standard model, the spectrum of propagated primary CR electrons at energies $\geq 30$ GeV softens with the increase of energy. The absence of any evidence for such a continuous spectral softening in $\Delta \Phi$ strongly suggests a significant `excess' of primary CR electrons and at energies of $100-400$ GeV the identified excess component has a flux comparable to that of the observed positron excess. Middle-age but `nearby' supernova remnants (e.g., Monogem and Geminga) are favored sources for such an excess.