The Imprint of Large Scale Structure on the Ultra-High-Energy Cosmic Ray Sky

Abstract

Ultra-high-energy cosmic rays (UHECRs) are atomic nuclei from space with vastly higher energies than any other particles ever observed. Their origin and chemical composition remain a mystery. As we show here, the large- and intermediate-angular-scale anisotropies observed by the Pierre Auger Observatory are a powerful tool for understanding the origin of UHECRs. Without specifying any particular production mechanism, but only postulating that the source distribution follows the matter distribution of the local Universe, a good accounting of the magnitude, direction and energy dependence of the dipole anisotropy at energies above $8\times 10^{18}$ eV is obtained, after taking into account the impact of energy losses during propagation (the "GZK horizon"), diffusion in extragalactic magnetic field and deflections in the Galactic magnetic field (GMF). This is a major step toward the long-standing hope of using UHECR anisotropies to constrain UHECR composition and magnetic fields. The observed dipole anisotropy is incompatible with a pure proton composition in this scenario. With a more accurate treatment of energy losses, it should be possible to further constrain the cosmic-ray composition and properties of the extragalactic magnetic field, self-consistently improve the GMF model, and potentially expose individual UHECR sources.

Accepted by the Astrophysical Journal Letters

References in corpus (11)

• Observation of a Large-scale Anisotropy in the Arrival Directions of Cosmic Rays above $8\times 10^{18}$ eV
• The Laniakea supercluster of galaxies
• Measurement of the cosmic-ray energy spectrum above $2.5\times 10^{18}$ eV using the Pierre Auger Observatory
• Features of the energy spectrum of cosmic rays above $2.5\times 10^{18}$ eV using the Pierre Auger Observatory
• Propagation of high-energy cosmic rays in extragalactic turbulent magnetic fields: resulting energy spectrum and composition
• The optical depth of the Universe to ultrahigh energy cosmic ray scattering in the magnetized large scale structure
• The Galactic Magnetic Field and Ultrahigh-Energy Cosmic Ray Deflections
• Cosmicflows-3: The South Pole Wall
• The extragalactic ultra-high energy cosmic-ray dipole
• Full-sky searches for anisotropies in UHECR arrival directions with the Pierre Auger Observatory and the Telescope Array
• Progress in the Global Modeling of the Galactic Magnetic Field

Cited by in corpus (28)

• Ultra-High-Energy Cosmic Rays: The Intersection of the Cosmic and Energy Frontiers
• Constraining models for the origin of ultra-high-energy cosmic rays with a novel combined analysis of arrival directions, spectrum, and composition data measured at the Pierre Auger Observatory
• What can be learnt from UHECR anisotropies observations? Paper I : large-scale anisotropies and composition features
• Active Galactic Nuclei as potential Sources of Ultra-High Energy Cosmic Rays
• Large-scale cosmic ray anisotropies with 19 years of data from the Pierre Auger Observatory
• UHECR mass composition at highest energies from anisotropy of their arrival directions
• Constraints on UHECR sources and extragalactic magnetic fields from directional anisotropies
• Impact of Galaxy Clusters on UHECR propagation
• Stellar Mass and Star Formation Rate within a Billion Light-Years
• Ultra High Energy Cosmic Ray Source Models: Successes, Challenges and General Predictions
• 2022 report from the Auger-TA working group on UHECR arrival directions
• Magnetically Induced Anisotropies in the Arrival Directions of Ultra-high-energy Cosmic Rays from Nearby Radio Galaxies
• What can be learnt from UHECR anisotropies observations Paper II: intermediate-scale anisotropies
• Treasure Maps for Detections of Extreme Energy Cosmic Rays
• The large-scale anisotropy and flux (de-)magnification of ultra-high-energy cosmic rays in the Galactic magnetic field
• Case for Centaurus A as the main source of ultrahigh-energy cosmic rays
• Revisiting the implications of Liouville's theorem to the anisotropy of cosmic rays
• Ultra-high-energy Cosmic Ray Sources can be Gamma-ray Dim
• Modification of the Dipole in Arrival Directions of Ultra-high-energy Cosmic Rays due to the Galactic Magnetic Field
• Constraining ultra-high-energy cosmic ray composition through cross-correlations
• A Heavy-Metal Scenario of Ultra-High-Energy Cosmic Rays
• Model-independent Evidence for an Increase in the Mean Mass of Cosmic Rays above 3 EeV
• Multimessenger Potential of the Radio Neutrino Observatory in Greenland
• Update on the indication of a mass-dependent anisotropy above $10^{18.7}$eV in the hybrid data of the Pierre Auger Observatory
• Revisiting Propagation Delays of Ultra-High-Energy Cosmic Rays from Long-lived Sources
• Explaining the UHECR spectrum, composition and large-scale anisotropies with radio galaxies
• Neutrino anisotropy as a probe of extreme astrophysical accelerators
• Probing extreme astrophysical accelerators through neutrino anisotropy