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The Pierre Auger Observatory (PAO) and Telescope Array (TA) collaborationsreport significant differences in the observed energy spectra ofultra-high-energy cosmic rays (UHECRs) above 30~EeV. In this work we present ajoint fit of TA and PAO data using the rigidity-dependent maximum energy model,including a full marginalization over all relevant parameters. We test twopossible scenarios to explain these differences. One is that they are due tocomplex energy-dependent experimental systematics; the other is the presence ofa local astrophysical source in the Northern Hemisphere, which is only visibleby the TA experiment. We show that the astrophysical and systematic scenariosimprove the explanation of the data equally well, compared to the scenariowhere both experiments observe the same UHECR flux from a cosmological sourcedistribution and have energy-independent systematics. We test different masscompositions emitted from the local source and conclude that the data are bestdescribed by a source lying at a distance below 26~Mpc that emits cosmic raysdominated by the silicon mass group. We also discuss possible sourcecandidates, and the possible role of the putative local UHECR source in theobserved TA anisotropy and in the differences in TA spectral data fromdifferent declination bands.

astrophysical journal/the astrophysical journal

Differences Between the Pierre Auger Observatory and Telescope Array  Spectra: Systematic Effects or Indication of a Local Source of  Ultra-High-Energy Cosmic Rays?