Cosmic-Ray Electron Excess from Pulsars is Spiky or Smooth?: Continuous and Multiple Electron/Positron injections

TL;DR

This paper analyzes how pulsars contribute to cosmic-ray electron and positron spectra, exploring whether their emissions are smooth or spiky, and discusses implications for source characteristics and future observations.

Contribution

It provides a detailed comparison of continuous versus multiple injections from pulsars and their effects on observed spectra, highlighting the need for specific pulsar properties to explain certain features.

Findings

Average pulsar contributions match current data

Single energetic pulsars are needed for the 500GeV peak

Source duration constrained to less than 10^5 years

Abstract

We investigate the observed spectrum of cosmic-ray electrons and positrons from astrophysical sources, especially pulsars, and the physical processes for making the spectrum spiky or smooth via continuous and multiple electron/positron injections. We find that (1) the average electron spectrum predicted from nearby pulsars are consistent with PAMELA, Fermi and H.E.S.S. data. However, the ATIC/PPB-BETS peak around 500GeV is hard to produce by the sum of multiple pulsar contributions and requires a single (or a few) energetic pulsar(s). (2) A continuous injection produces a broad peak and a high energy tail above the peak, which can constrain the source duration ($\lesssim 10^5$yr with the current data). (3) The H.E.S.S. data in the TeV range suggest that young sources with age less than $\sim 6 \times 10^4$yr are less energetic than $\sim 10^{48}{\rm erg}$. (4) We also expect a large dispersion in the TeV spectrum due to the small number of sources, that may cause the high energy cutoff inferred by H.E.S.S. and potentially provide a smoking-gun for the astrophysical origin. These spectral diagnostics can be refined in the near future by the CALET experiments to discriminate different astrophysical and dark matter origins.