The universe is home to extreme environments that emit incredibly high-energy particles. Sources such as supernova remnants, pulsars, and active galactic nuclei generate particles and gamma rays far exceeding the energy produced by nuclear fusion in stars. Gamma rays provide valuable information about these sources, traveling undisturbed through space. However, charged cosmic rays like electrons and positrons interact with magnetic fields and light, losing energy during their journey and making it impossible to pinpoint their origin.
Cosmic-ray electrons (CRe) with energies exceeding one TeV are especially rare and challenging to detect. Space-based instruments lack the sensitivity for these particles due to their small detection areas. Ground-based observatories, like H.E.S.S., face difficulties distinguishing the particle showers caused by electrons or positrons from the more common showers from cosmic-ray protons and nuclei. Using its five telescopes, H.E.S.S. records faint Cherenkov radiation from particle showers in the Earth's atmosphere, primarily to study gamma-ray sources. However, its data can also be adapted to search for high-energy cosmic-ray electrons.
The H.E.S.S. collaboration achieved this by analyzing a decade's worth of data from its 12-meter telescopes. Employing advanced algorithms, the team efficiently isolated CRe signals from background noise, producing a highly detailed dataset on cosmic-ray electrons. This analysis extended to energy levels up to 40 TeV and revealed an unexpected, sharp break in the CRe energy spectrum.
"This is an important result, as we can conclude that the measured CRe most likely originate from very few sources in the vicinity of our own solar system, up to a maximum of a few 1000 light years away, a very small distance compared to the size of our Galaxy," said Kathrin Egberts, University of Potsdam.
"We were able to put severe constraints on the origin of these cosmic electrons with our detailed analysis for the first time," added Prof. Werner Hofmann of the Max-Planck-Institut fur Kernphysik. Mathieu de Naurois, a CNRS researcher, emphasized that "our measurement does not only provide data in a crucial and previously unexplored energy range, impacting our understanding of the local neighborhood, but it is also likely to remain a benchmark for the coming years."
This groundbreaking study highlights the capability of ground-based observatories like H.E.S.S. to probe the universe's most extreme energy ranges, advancing the understanding of cosmic accelerators and their proximity to Earth.
Research Report:High-Statistics Measurement of the Cosmic-Ray Electron Spectrum with H.E.S.S.
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H.E.S.S. collaboration
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