Galactic factories of cosmic-ray electrons and positrons

TL;DR

This paper models the spectrum of cosmic-ray electrons and positrons from Galactic sources like supernova remnants and pulsars, revealing features that explain observed spectra and positron fractions, emphasizing the importance of source distribution and evolution.

Contribution

It introduces a novel, detailed model of electron and positron spectra considering time-dependent pulsar emissions and source distributions within the Galaxy's spiral arms.

Findings

Electron spectrum shows a feature at >50 GeV due to radiative losses.

Positron spectrum and rising fraction are well explained by pulsar contributions.

Fluctuations impact high-energy spectra, affecting source identification.

Abstract

We present a novel calculation of the spectrum of electrons and positrons from random sources, supernova remnants and pulsars, distributed within the spiral arms of the Galaxy. The pulsar emissivity in terms of electron-positron pairs is considered as time dependent, following the magnetic dipole spin-down luminosity, and the temporal evolution of the potential drop is accounted for. Moreover each pulsar, with the magnetic field and initial spin period selected at random from the observed distribution, is considered as a source of pairs only after it leaves the parent supernova due to its birth kick velocity (also selected at random from the observed distribution). We show that (i) the spectrum of electrons is characterized by a feature at $\gtrsim 50$ GeV that proves that their transport is dominated by radiative losses. The flux reduction at $E\gtrsim 1$ TeV is explained as a result of lepton transport from sources in the spiral arms. (ii) The spectrum of positrons is very well described by the contribution of pulsars and the rising positron fraction originates naturally. The implications of pulsars as positron sources in terms of positron fraction at very high energies are also discussed. (iii) The role of fluctuations in the high-energy regime is thoroughly discussed and used to draw conclusions on the possibility to single out the contribution of local sources to the lepton spectrum with current and upcoming experiments.