G. Giacinti, M. Kachelriess, D. V. Semikoz, G. Sigl
We constrain the energy at which the transition from Galactic to
extragalactic cosmic rays occurs by computing the anisotropy at Earth of cosmic
rays emitted by Galactic sources. Since the diffusion approximation starts to
loose its validity for E/Z >~ 10^(16-17) eV, we propagate individual cosmic
rays using Galactic magnetic field models and taking into account both their
regular and turbulent components. The turbulent field is generated on a nested
grid which allows spatial resolution down to fractions of a parsec. If the
primary composition is mostly light or intermediate around E ~ 10^18 eV, the
transition at the ankle is ruled out, except in the unlikely case of an extreme
Galactic magnetic field with strength >~ 10 {\mu}G. Therefore, the fast rising
proton contribution suggested by KASCADE-Grande data between 10^17 eV and 10^18
eV should be of extragalactic origin. In case heavy nuclei dominate the flux at
E >~ 10^18 eV, the transition energy can be close to the ankle, if Galactic
cosmic rays are produced by sufficiently frequent transients as e.g. magnetars.
View original:
http://arxiv.org/abs/1112.5599
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