High-Statistics Measurement of the Cosmic-Ray Electron Spectrum with H.E.S.S

TL;DR

This paper reports a high-precision measurement of cosmic-ray electrons from 0.3 to 40 TeV using H.E.S.S., revealing a spectral break around 1 TeV and constraining local cosmic-ray sources and propagation models.

Contribution

It provides the first high-statistics spectrum of cosmic-ray electrons over a wide energy range with improved proton rejection, identifying a spectral break at 1 TeV.

Findings

Spectral break at ~1 TeV with increased spectral index

Proton rejection power better than 10^4

Spectrum is featureless apart from the break

Abstract

Owing to their rapid cooling rate and hence loss-limited propagation distance, cosmic-ray electrons and positrons (CRe) at very high energies probe local cosmic-ray accelerators and provide constraints on exotic production mechanisms such as annihilation of dark matter particles. We present a high-statistics measurement of the spectrum of CRe candidate events from 0.3 to 40 TeV with the High Energy Stereoscopic System (H.E.S.S.), covering two orders of magnitude in energy and reaching a proton rejection power of better than $10^{4}$. The measured spectrum is well described by a broken power law, with a break around 1 TeV, where the spectral index increases from $\Gamma_1 = 3.25$ $\pm$ 0.02 (stat) $\pm$ 0.2 (sys) to $\Gamma_2 = 4.49$ $\pm$ 0.04 (stat) $\pm$ 0.2 (sys). Apart from the break, the spectrum is featureless. The absence of distinct signatures at multi-TeV energies imposes constraints on the presence of nearby CRe accelerators and the local CRe propagation mechanisms.