Extragalactic magnetic fields and the second knee in the cosmic-ray spectrum

Recent work suggests that the cosmic-ray spectrum may be dominated by Galactic sources up to ~1017.5 eV, and by an extra-Galactic component beyond, provided this latter cuts off below the transition energy. Here it is shown that this cut-off could be interpreted in this framework as a signature of extra-galactic magnetic fields with equivalent average strength B and coherence length lc such that $B√{{l}c}{~}2{-}3·{}{10}^{{-}10} G·{}{Mpc}1/2$, assuming ${l}c<{r}L$ (Larmor radius at ${}{10}¹⁷$ eV) and continuously emitting sources with density ${10}^{{-}5}{ Mpc}^{{-}3}$. The extra-Galactic flux is suppressed below ${~}{10}¹⁷$ eV as the diffusive propagation time from the source to the detector becomes larger than the age of the Universe.