The energy spectrum of ultra-high energy cosmic rays measured at the Pierre Auger Observatory and at the Telescope Array

TL;DR

This paper compares the ultra-high energy cosmic ray spectra measured by the Pierre Auger Observatory and the Telescope Array, highlighting differences and systematic uncertainties in their energy measurements and spectral features.

Contribution

It provides a detailed analysis of the spectral differences between the two major UHECR observatories, considering energy-dependent uncertainties and sky coverage effects.

Findings

Both observatories observe a steepening of the spectrum above tens of EeV.

Significant differences exist in the spectra that cannot be explained by energy scale uncertainties.

Analysis of spectral features helps improve understanding of measurement discrepancies.

Abstract

The energy spectrum of ultra-high energy cosmic rays (UHECRs) provides essential information on the most energetic phenomena in the Universe. Beyond EeV energies, the Telescope Array and Pierre Auger Observatory have the largest exposures to UHECRs ever accumulated in the Northern and Southern hemispheres, respectively. The results show independently a steepening of the energy spectrum above a few tens of EeV. However, the comparison of the spectra shows differences that are not explainable in terms of an overall uncertainty on the energy scale used to reconstruct the extensive air showers. The differences are also observed in the region of the sky covered by both instruments, where the spectra should be in agreement within uncertainties when directional-exposure effects are accounted for. For this contribution, a working group from both collaborations examined these differences considering the energy-dependent systematic uncertainties. A special focus is given to the characterization of the spectral features, which provide an accurate tool to enhance our understanding of the comparisons.