Astronomy & Astrophysics Seminar: On the Origin of the Ultra-high Energy Cosmic Rays

Abstract: 

Cosmic-rays are one of the most fascinating, yet surprisingly common, phenomena in the universe. They consist of energetic particles with an out-of-equilibrium power-law spectrum extending over at least eleven orders of magnitude in energy, from ~1 GeV to 10^11 GeV. In the past few years, new measurements  by experiments such as KASCADE-Grande, the Pierre Auger observatory and Telescope Array, have greatly improved our knowledge of the highest energy domain of the cosmic-ray spectrum. Recent Auger composition analyses suggest a composition getting gradually heavier above a few 10^18 eV. I  review the recent observations and  show that the observational data can be explained by a generic model having only one Galactic component and one extragalactic component. The key to the success of this model is that the protons emitted by the extragalactic sources have a different spectrum from the other types of nuclei, as we recently showed to be expected in highly magnetised and photon-rich environments, such as the relativistic jets associated with GRB or AGN. I will discuss multi-messenger constrains brought by neutrino and gamma-ray experiments and discuss the possible extragalactic origin of the UHECR dipole anisotropy, recently reported by Auger.

Seminar Organizer: Prof. Sara Beck