Large-scale Cosmic-Ray Anisotropies above 4 EeV Measured by the Pierre Auger Observatory

Authors

• G. R. Snow, University of Nebraska - Lincoln

Document Type

Article

Date of this Version

2018

Citation

The Astrophysical Journal, 868:4 (12pp)

Comments

© 2018. The American Astronomical Society.

https://doi.org/10.3847/1538-4357/aae689

Abstract

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 β = 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.