A New Limit on the Distances of Nuclei UHECRs Sources

Understand

Recent evidence from the Pierre Auger Observatory suggests a transition, at 5 EeV-10EeV in the composition of Ultra High Energy Cosmic Rays (UHECRs), from protons to heavier nuclei such as iron.

• I consider here the implications of the heavier composition on the sources of UHECRs.
• The smaller magnetic rigidity implies that nuclei UHECRs are: (i) More easily accelerated (ii) Local, as they can diffuse only a few Mpc from their sources before disintegrating (iii) Isotropic, because large deflections in the extra galactic and the galactic magnetic fields erase the directional information.
• Uncertainties in the strength and structure of the the extra galactic magnetic field (EGMF) makes it difficult to estimate the overall effects.