The `excess' of primary cosmic ray electrons

Abstract

With the accurate cosmic ray (CR) electron and positron spectra (denoted as ${\Phi }_{{\mathrm{e}}^{-}}$ and ${\Phi }_{{\mathrm{e}}^{+}}$, respectively) measured by AMS-02 collaboration, the difference between the electron and positron fluxes (i.e., $\Delta \Phi ={\Phi }_{{\mathrm{e}}^{-}}-{\Phi }_{{\mathrm{e}}^{+}}$), dominated by the propagated primary electrons, can be reliably inferred. In the standard model, the spectrum of propagated primary CR electrons at energies $\ge 30$ 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.

Comments: 13 pages, 2 figures, Phys. Lett. B, in press