Interpretation of ultra-high energy multi-messenger data

Charged ultra-high energy cosmic rays above ∼1017 eV are most likely accelerated in powerful astrophysical objects that have to meet a number of requirements to reach energies beyond the highest energies observed, a few 1020 eV, among them sufficient electromagnetic power and further constraints on geometry and magnetic fields to avoid excessive energy losses during acceleration. Since charged particles are deflected in cosmic magnetic fields and do not always point back to their sources, it is challenging to identify them and to reconstruct a detailed understanding of the acceleration mechanism. Neutral secondaries such as γ−rays and neutrinos that are produced by interactions of primary cosmic rays within the source and during propagation can provide important complementary information. We provide a brief overview over how multi-messenger data can be exploited to learn more about source and propagation physics