Towards Understanding the Origin of Cosmic-Ray Electrons

Abstract

Precision results on cosmic-ray electrons are presented in the energy range from 0.5 GeV to 1.4 TeV based on $28.1\times 10^{6}$ electrons collected by the Alpha Magnetic Spectrometer on the International Space Station. In the entire energy range the electron and positron spectra have distinctly different magnitudes and energy dependences. The electron flux exhibits a significant excess starting from $42.1^{+5.4}_{−5.2} $ GeV compared to the lower energy trends, but the nature of this excess is different from the positron flux excess above $25.2 \pm 1.8$  GeV. Contrary to the positron flux, which has an exponential energy cutoff of $810^{+310}_{−180}$  GeV, at the 5σ level the electron flux does not have an energy cutoff below 1.9 TeV. In the entire energy range the electron flux is well described by the sum of two power law components. The different behavior of the cosmic-ray electrons and positrons measured by the Alpha Magnetic Spectrometer is clear evidence that most high energy electrons originate from different sources than high energy positrons.

Supplemental Material
Download AMS Data

The electron flux $\Phi_{e^-}$ as a function of the energy at the top of AMS. Characteristic energy $\tilde{E}$ (i.e. spectrally weighted mean energy in the bin) is given with its systematic error from the energy scale uncertainty. The number of electron events before unfolding, $N_{e^−}$, is given together with its statistical error from the fit. $\sigma_{\rm stat}^{e^-}$ is the statistical and $\sigma_{\rm syst}^{e^-}$ is the total systematic error of the electron flux.
 

Table-SII

Download the Table

The combined (electron + positron) flux ($\Phi_{e^-}+\Phi_{e^+}$) and positron fraction ${\rm PF} \equiv \Phi_{e^+}/\left(\Phi_{e^-}+\Phi_{e^+}\right)$ as a function of the energy at the top of AMS. The systematic errors of the combined (electron + positron) flux and the positron fraction account for correlations related to the calculation of the acceptance.

External Databases

The CRDB © SSDC is developed at the Space Science Data Center, a facility of the Italian Space Agency (ASI).