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Magnetic horizons of UHECR sources and the GZK feature

2004; Elsevier BV; Volume: 21; Issue: 6 Linguagem: Inglês

10.1016/j.astropartphys.2004.04.012

1873-2852

Olivier Deligny, A. Letessier‐Selvon, Ètienne Parizot,

Neutrino Physics Research

We study the effect of random extra-galactic magnetic fields on the propagation of protons of energy larger than $10^{19}$ eV. We show that for reasonable field values (in the 100 nG range) the transition between diffusive and ballistic regimes occurs in the same energy range as the GZK cutoff (a few $10^{19}$ eV). The usual interpretation of the flux reduction above the GZK energy in terms of a sudden reduction of the visible horizon is modified. Moreover, since the size of the diffusion sphere of a continuous source of cosmic rays is of the order of 10 Mpc, the local structure of the Universe and therefore of potential local astrophysical sources plays a dominant role in the expected spectrum. Under reasonable assumptions on the sources configurations the expected GZK cutoff is reduced.