Gamma-ray astronomy and the challenges of standard Galactic cosmic-ray models

Le 19 septembre 2025, Luigi Tibaldo, 10h45 à 11h45, Salle Jules Verne, OMP, site Belin

Summary: Cosmic rays are energetic particles first observed around the Earth with energies ranging from MeV to above 10^20 eV and with approximately isotropic arrival directions. A most remarkable change of the cosmic-ray spectrum occurs around 10^15 eV. Below this energy, the standard paradigm holding since the sixties assumes that the particles originate in the Milky Way, very likely from shock acceleration in supernova remnants, and diffuse on turbulent magnetic fields in a kpc-sized halo encompassing the disk of the Galaxy for several Myr. However, several recent measurements of exquisite precision challenge these standard Galactic cosmic-ray models. In this seminar I will give an overview of the research in the field and focus on two pressing questions from the perspective of observations in the gamma-ray band. Are supernova remnants the only or main sources of Galactic cosmic rays? Are discrepancies between observations and predictions from standard transport models due to missing details or do they require fundamental paradigm changes?