通俗演講

2021/02/02(Tue)     14:00 -16:00    一樓演講廳1st Floor(auditorium)

Title

Multimessenger sources of ultra-high energy cosmic ray nuclei and astrophysical neutrinos

Speaker

Dr. Anatoli Fedynitch

Institute for Cosmic Ray Research (ICRR), The University of Tokyo, Japan

Abstract

The universe hosts particle accelerators that emit cosmic ray nuclei with energies in excess of 1021 eV. The nature of these accelerators is still elusive and neither the environment nor the acceleration principle is exactly known, but that the observed events at the highest energies are nuclei is experimentally (almost) certain. The list of astrophysical source candidates includes the most violent cosmic objects, such as the relativistic outflows (jets) of exploding massive stars (Gamma-Ray Bursts) or supermassive black holes at galaxy centers (Blazars). Through (photo-)hadronic interactions with ambient light or matter, protons or nuclei can produce secondary messengers, photons and neutrinos, within the source or on their intergalactic trip to Earth. The current generation of the IceCube Neutrino Observatory aimed to detect these very faint signals but the sensitivity turned out to be too weak, yet, to resolve significant (point-like) sources. However, several strong arguments have been derived about populations of source candidates using data from diffuse observations, leading to progress in the field during the last decade and showing a clearer path forward. In this talk I will introduce the challenges in identifying the chemical composition of UHECR originating from the modelling of hadronic interactions, and then focus on the physics of nuclei and neutrino emission in the sources and during propagation.