International School of Cosmic Ray Astrophysics <<Maurice M. Shapiro>>

21^st Course: Astroparticle Physics: Yesterday, Today, and Tomorrow
1-7 August, 2018

At very high energies cosmic-ray electrons loose their energy rapidly by inverse Compton scattering and synchrotron radiation. These radiative losses limit their lifetime and propagation distance. The spectrum of multi-TeV electrons thereby provides unique insights in the activity of particle accelerators in our local neighbourhood. The very low fluxes and the large background of hadronic cosmic rays however impose severe challenges to both space-born and ground-based measurements. The next generation satellite experiments are just starting to probe this energy regime. They will still need a couple of years to gain the statistics needed for precision measurements. Ground-based instruments with their five orders of magnitude larger effective collection areas on the other hand accumulate the necessary statistics easily and are ideally suited for measurements in this energy range. The indirect detection of cosmic-ray electrons with imaging atmospheric Cherenkov telescopes requires a superb separation of the excessive hadronic background and is therefore prone to systematic errors. New developments have now allowed for the first time a measurement of the cosmic-ray electron spectrum up to 20 TeV and a significant reduction of its systematic uncertainties. In this lecture I will review our current knowledge of the cosmic-ray electron spectrum at TeV energies, describe the techniques that have led to this big leap forward and discuss the implications of these measurements.