Extra-galactic magnetic fields and the second knee in the cosmic-ray spectrum
Abstract
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 Blc ~ 2-3.10-10 G.Mpc1/2, assuming lc < rL (Larmor radius at 1017 eV) and continuously emitting sources with density 10-5/Mpc3. The extra-Galactic flux is suppressed below 1017 eV as the diffusive propagation time from the source to the detector becomes larger than the age of the Universe.
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