LAM seminar: Pierre Cristofari – Very high-energy gamma-ray astronomy and the origin of cosmic rays

Cosmic rays are relativistic charged particles, mainly protons, that arrive to Earth from all directions of the sky. Despite extensive precision measurements from numerous cosmic ray observatories, the question of their origin remains unanswered. The difficulty of identifying the sources lies fundamentally in the fact that cosmic rays are deflected by Galactic and extragalactic magnetic fields during their propagation, and thus, when they reach us, the direction of arrival does not point back to the sources.

Close to the sites of particle acceleration, cosmic rays interact with the interstellar medium (nuclei, magnetic fields) to produce photons, from the radio to the very-high-energy gamma-ray domain. The very-high-energy gamma-ray domain (TeV = 10¹² eV) can directly help probe particle acceleration at the highest energies.

Observations with ground-based Cherenkov telescopes have already revealed hundreds of TeV gamma-ray sources. In the coming years, the new generation of gamma-ray observatories, such as LHAASO and CTAO, will offer a new view of the gamma-ray sky and will help close in on the problem of the origin of cosmic rays.