What can be learnt from UHECR anisotropies observations Paper II: intermediate-scale anisotropies

Abstract

Analysing the available data relative to the anisotropies of the ultra-high-energy cosmic rays (UHECR) at intermediate angular scales, we examine to what extent they can be used to constrain the origin of these particles, and what could be gained from a new generation of observatories with increased exposure. We simulate realistic UHECR sky maps for a wide range of scenarios, with the assumption that the distribution of UHECR sources follows that of matter in the Universe, also considering possible biases. We produce numerous datasets on which we apply similar analyses as those recently used by the Auger and TA collaborations. We find that: i) the investigated scenarios can easily account for the significance of the anisotropies reported by Auger and TA; ii) the direction in which the maximum flux excess is found in the Auger data differs from where it is found in most of our simulations; iii) for datasets simulated with the same astrophysical scenario, the significance with which the isotropy hypothesis is rejected through the Auger likelihood analysis can be largest either when "all galaxies" or when "starburst" galaxies are used to model the signal, depending on which GMF model is used; iv) the study of the energy evolution of the anisotropy patterns can provide new insight about the origin of UHECRs; v) the direction in which the most significant flux excess is found in the Auger dataset above 8 EeV appears to essentially disappear in the dataset above 32 EeV; vi) this appears to be very uncommon in our simulations, which could point to a failure of some generic assumption in the investigated scenarios, such as the predominance of a unique type of sources in the flux above the ankle, with essentially the same composition and spectrum; vii) a meaningful measurement of their energy evolution, from 10 EeV to the highest energies, will require a significant increase in statistics.

arXiv comment29 pages, 23 figures - Sects. 4.2 and 4.3 rewritten to make the quantitative comparison between the simulations and Auger data clearer - Discussion on TA anisotropies moved to the Appendix - A short discussion on the impact of more recent Galactic magnetic models added at the end of the paper. - No change in the discussions and conclusions. - To appear in Astronomy and Astrophysics

References in corpus (39)

• HEALPix -- a Framework for High Resolution Discretization, and Fast Analysis of Data Distributed on the Sphere
• Correlation of the highest energy cosmic rays with nearby extragalactic objects
• The 2MASS Redshift Survey - Description and Data Release
• A New Model of the Galactic Magnetic Field
• HCN Survey of Normal Spiral, IR-luminous and Ultraluminous Galaxies
• Observation of a Large-scale Anisotropy in the Arrival Directions of Cosmic Rays above $8\times 10^{18}$ eV
• The surface detector array of the Telescope Array experiment
• GeV Observations of Star-forming Galaxies with \textit{Fermi} LAT
• Radio observational constraints on Galactic 3D-emission models
• 3FHL: The Third Catalog of Hard Fermi-LAT Sources
• Indications of Intermediate-Scale Anisotropy of Cosmic Rays with Energy Greater Than 57 EeV in the Northern Sky Measured with the Surface Detector of the Telescope Array Experiment
• Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter
• The Galactic Magnetic Field
• The Laniakea supercluster of galaxies
• The Giant Radio Array for Neutrino Detection (GRAND): Science and Design
• Indication of anisotropy in arrival directions of ultra-high-energy cosmic rays through comparison to the flux pattern of extragalactic gamma-ray sources
• Galaxy Groups within 3500 km s${}^{-1}$
• Searches for Anisotropies in the Arrival Directions of the Highest Energy Cosmic Rays Detected by the Pierre Auger Observatory
• Mid- and Far-infrared Luminosity Functions and Galaxy Evolution from Multiwavelength Spitzer Observations up to z~2.5
• Anisotropy vs chemical composition at ultra-high energies
• The Galactic halo magnetic field revisited
• The quenching of the star formation activity in cluster galaxies
• Propagation of ultrahigh energy nuclei in clusters of galaxies: resulting composition and secondary emissions
• Radio galaxies of the local universe: all-sky catalog, luminosity functions, and clustering
• Ultra-High-Energy Cosmic Rays: The Intersection of the Cosmic and Energy Frontiers
• Arrival Directions of Cosmic Rays above 32 EeV from Phase One of the Pierre Auger Observatory
• IMAGINE: A comprehensive view of the interstellar medium, Galactic magnetic fields and cosmic rays
• The star formation history of galaxies: the role of galaxy mass, morphology and environment
• Fornax A, Centaurus A and other radio galaxies as sources of ultra-high energy cosmic rays
• The Imprint of Large Scale Structure on the Ultra-High-Energy Cosmic Ray Sky
• Ultrahigh Energy Nuclei Propagation in a Structured, Magnetized Universe
• Ultrahigh energy cosmic rays from a nearby extragalactic source in the diffusive regime
• Galactic and Extragalactic Magnetic Fields
• The quasi-linear nearby Universe
• What can be learnt from UHECR anisotropies observations? Paper I : large-scale anisotropies and composition features
• Anisotropy expectations for ultra-high-energy cosmic rays with future high statistics experiments
• GCOS -- The Global Cosmic Ray Observatory
• Are starburst galaxies a common source of high energy neutrinos and cosmic rays?
• Progress in the Global Modeling of the Galactic Magnetic Field

Cited by in corpus (2)

• Modeling Ultra-High-Energy Cosmic Rays propagation using the input from Configuration Interaction Shell Model
• Displacement of ultra-high-energy cosmic ray source images by the intergalactic magnetic field: the cases of Cen A and M83