Study of Galactic interactions and propagation properties of ultrahigh energy cosmic rays using the precision spectrum from the Pierre Auger Observatory

Abstract

The AUGER Collaboration has recently published the precise energy spectrum of cosmic rays above 1 EeV, which exhibits rich and interesting features. These features provide an opportunity to investigate the galactic propagation and interaction of ultra-high-energy cosmic rays (UHECRs). While the classic dip model, which describes the UHECR propagation and interaction with CMB in extragalactic space by theoretical calculation, well explains the cutoff behaviour of the highest high energy spectrum of AUGER, it fails to describe the low energy features. It indicates that the galactic propagation and interaction of UHECR might play an important role in modulating the low energy side of AUGER spectrum. With the disk-halo diffusion model, this work demonstrates excellent agreement with the energy spectrum measured by AUGER and supports that the diffusion coefficient follows a power-law with an index of $1.81^{+0.05}_{-0.04}$ in the galaxy at least above $5\times10^{18}$eV. The inferred diffusion coefficient is one to two order of magnitude smaller than these extrapolated from low energy studies when conventional model parameters are adopted. Study of the modulation effect at cluster of galaxy level might be needed.