Ultra high energy cosmic rays and the Galactic halo

An analysis has been made of the fraction of ultra high energy cosmic rays (above 10(18) eV) which could be due to processes involved in two possible 'Models'. The first is the Giant Magnetic Halo Model and the second is the Dark Matter Halo Model. We find that the former, in which heavy nuclei are trapped in a giant halo, fails for energies above about 3 x 10(19) eV. For the Dark Matter Halo Model, in which relic particles follow the "convention al" dark matter and whose decays give ultra high energy cosmic rays, the pr edicted anisotropies are much higher than those observed. The lack of obser vation of a finite flux from the Andromeda Galaxy means that the conclusion is insensitive to the spatial scale size of the assumed halo distribution. It is concluded that less than 10% of the ultra high energy cosmic rays co me from relic particles in the Galactic halo. (C) 1999 Elsevier Science B.V .