Comparison of the Ultra-High Energy Cosmic Ray Flux Observed by AGASA, HiRes and Auger

Abstract

The current measurements of the cosmic ray energy spectrum at ultra-high energies ($\text{E}>10^{19}$ eV) are characterized by large systematic errors and poor statistics. In addition, the experimental results of the two experiments with the largest published data sets, AGASA and HiRes, appear to be inconsistent with each other, with AGASA seeing an unabated continuation of the energy spectrum even at energies beyond the GZK cutoff energy at $10^{19.6}$ eV. Given the importance of the related astrophysical questions regarding the unknown origin of these highly energetic particles, it is crucial that the extent to which these measurements disagree be well understood. Here we evaluate the consistency of the two measurements for the first time with a model-independent method that accounts for the large statistical and systematic errors of current measurements. We further compare the AGASA and HiRes spectra with the recently presented Auger spectrum. The method directly compares two measurements, bypassing the introduction of theoretical models for the shape of the energy spectrum. The inconsistency between the observations is expressed in terms of a Bayes Factor, a standard statistic defined as the ratio of a separate parent source hypothesis to a single parent source hypothesis. Application to the data shows that the two-parent hypothesis is disfavored. We expand the method to allow comparisons between an experimental flux and that predicted by any model.

arXiv commentaccepted by Phys. Rev. D

References in corpus (5)

• Energy determination in the Akeno Giant Air Shower Array experiment
• Measurement of the Flux of Ultrahigh Energy Cosmic Rays from Monocular Observations by the High Resolution Fly's Eye Experiment
• Monocular Measurement of the Spectrum of UHE Cosmic Rays by the FADC Detector of the HiRes Experiment
• On the statistical significance of the GZK feature in the spectrum of ultra high energy cosmic rays
• A closer look at the spectrum and small scale anisotropies of UHECRs

Cited by in corpus (7)

• High-energy neutrinos in the context of multimessenger physics
• LUNASKA experiments using the Australia Telescope Compact Array to search for ultra-high energy neutrinos and develop technology for the lunar Cherenkov technique
• The sensitivity of the next generation of lunar Cherenkov observations to UHE neutrinos and cosmic rays
• An Evolutionary Paradigm for Dusty Active Galaxies at Low Redshift
• Cosmology and Neutrino Properties
• Fossil AGN jets as ultra high energy particle accelerators
• Neutrino Properties, Cosmology