http://arxiv.org/abs/1709.07793
We examine limits to the energy to which cosmic rays can be accelerated by relativistic shocks, showing that acceleration of light ions as high as 100 EeV is unlikely. The implication of our estimates is that if ultra-high energy cosmic rays are accelerated by shocks, then those shocks are probably not relativistic.
A. Bell, A. Araudo, J. Matthews, et. al.
Mon, 25 Sep 17
60/60
Comments: Accepted for publication in Monthly Notices of the Royal Astronomical Society