Cosmic Magnetic Fields from the Perspective of Ultra-High-Energy Cosmic Rays Propagation

Abstract

The Ultra High Energy Cosmic Ray (UHECR) and Gamma Ray Burst (GRB) fields are very similar in many respects. Both have gone through a burst of activity in source modeling, both have a history of “repeaters” and, for both, the discovery of isotropy in arrival directions mean a fundamental change of current views and ideas. As in the case of gamma ray bursts (GRB), one can expect that the next significant step in our understanding of the UHECR problem will come when some source is finally identified as data accumulates from the new large exposure experiments under construction. However, UHECR are most likely charged particles, and so there is probably not such a thing as an easily identifiable optical counterpart, as there turned out to be with GRBs. Intervening galactic and intergalactic magnetic fields can affect propagation at energies of hundreds of EeV in a very significant way. This coupling means that both, cosmic magnetic fields and UHECR will have to be tackled together. UHECR will be, at the same time, the object of study and an invaluable diagnostic tool for magnetic fields inside the 100 Mpc sphere defined by the Greisen-Zatsepin-Kuzmin cut-off. The prospects for the future will be discussed.