Abstrakt
We present a detailed study of the large-scale anisotropies of cosmic rays with energies above 4 EeV measured using the Pierre Auger Observatory. For the energy bins [4, 8] EeV and E >= 8 EeV, the most significant signal is a dipolar modulation in R.A. at energies above 8 EeV, as previously reported.
In this paper we further scrutinize the highest-energy bin by splitting it into three energy ranges. We find that the amplitude of the dipole increases with energy above 4 EeV.
The growth can be fitted with a power law with index beta = 0.79 +/- 0.19. The directions of the dipoles are consistent with an extragalactic origin of these anisotropies at all the energies considered.
Additionally, we have estimated the quadrupolar components of the anisotropy: they are not statistically significant. We discuss the results in the context of the predictions from different models for the distribution of ultrahigh-energy sources and cosmic magnetic fields.