Astrophysics: Cosmic-ray electrons measured by ‘Monkey King’ satellite

The energy spectrum of cosmic-ray electrons and their antimatter counterparts, positrons, has been measured directly with unprecedentedly high energy resolution by the Dark Matter Particle Explorer (DAMPE) satellite. The findings, reported online in Nature, could add to efforts to understand the mysterious origins of certain cosmic-ray electrons and positrons.

Measuring the spectrum of high-energy cosmic-ray electrons and positrons provides insights into Galactic high-energy processes and may enable the observation of phenomena such as dark-matter particle annihilation, where the particles are converted to gamma rays, or decay. This spectrum has been measured directly only up to about two teraelectronvolts in previous balloon- or space-borne experiments and only indirectly up to about five teraelectronvolts using ground-based telescope arrays.

The Chinese DAMPE instrument, nicknamed ‘Wukong’ (Monkey King), is able to detect cosmic-ray electrons and positrons up to energies of about ten teraelectronvolts. Yi-Zhong Fan and colleagues from the DAMPE Collaboration report direct measurements in the energy range 25 gigaelectronvolts to 4.6 teraelectronvolts with extremely high energy resolution and low background. They also find a spectral break - a greater-than-expected drop in the number of cosmic-ray electrons and positrons seen at high energies - at about 0.9 teraelectronvolts, confirming previous indirect measurements.