Electrons account for only a small fraction, less than 1%, of cosmic rays arriving on Earth, yet they provide crucial insights into the acceleration, escape, and transport of cosmic rays within the Milky Way. Specific spectral signatures might also be associated with their production through the annihilation of dark matter particles, such as WIMPs. At high energies, electrons cannot travel incognito; they necessarily interact via synchrotron emission with interstellar magnetic fields and via inverse Compton scattering with radiation. In doing so, they rapidly lose energy. The short lifespan of cosmic electrons, combined with their chaotic trajectories in magnetic fields, imposes strict limits on the age and maximum distance of the accelerators producing them, thus revealing the presence of sources in the vicinity of the solar system.
Up to energies of about one Teraelectronvolt (TeV), the electron spectrum is measured precisely from space, particularly by experiments like AMS, CALET, or DAMPE. However, the data from these instruments are not entirely consistent with one another. At higher energies, the fluxes become so low that very large instruments are required for their detection. Atmospheric Cherenkov Telescopes, which detect particle cascades developing in the upper atmosphere through the Cherenkov radiation emitted by charged particles, can then take over. However, these instruments are designed for studying gamma rays emitted by localized sources in space and are limited by the so-called "hadronic" background noise produced by protons and nuclei, which are far more abundant in cosmic rays.
The H.E.S.S. (High Energy Stereoscopic System) array in Namibia consists of four 12-meter-diameter telescopes and one 28-meter telescope. By analyzing over 3,000 hours of off-Galactic-plane observations, we were able to precisely study the cosmic electron spectrum up to energies close to 40 Teraelectronvolts, a record to date. The results of this study will be presented during the seminar, along with their implications: The cosmic electron spectrum is characterized by a very distinct spectral break at an energy around one Teraelectronvolt. This strongly suggests that a handful of very nearby and very young sources—or even a single source—located within ~300 pc of Earth is responsible for the ultra-high-energy electrons reaching Earth.
zoom connection: https://cern.zoom.us/j/68399739111?pwd=SGErcHBQYmVLWFZTVE9jdm5xSmdEdz09
François Brun, Matthias Saimpert
