Due to their small masses, TeV cosmic-ray (CR) electrons suffer severe radiative losses, which drastically reduce their lifetime and propagation distance. Consequently, the CR electron spectrum at > TeV energies strongly depends on local conditions and is expected to be highly variable throughout the Galaxy. The radiative losses furthermore result in a steepening of the spectrum in absence of replenishing electron accelerators.
A measurement of CR electrons at TeV energies and beyond is increasingly challenging for satellite experiments because of this steep spectrum and the low fluxes. This is the regime where imaging atmospheric Cherenkov telescopes with their approximately five orders of magnitude higher collection areas can make a difference. By exploiting improved hadron-rejection capabilities, the High Energy Stereoscopic System (H.E.S.S.) has now extended the measured spectrum of our local CR electrons to ~20 TeV. This measurement explores a previously completely unknown energy range and enters the regime at which secondary electrons start to dominate the CR electron spectrum - the end point for any primary CR electron measurement.
This presentation will review the new H.E.S.S. measurement of the CR electron spectrum and discuss some of its implications for local accelerators as well as future measurements.