Measurements and implications of cosmic ray anisotropies from TeV to trans-EeV energies

TL;DR

This review summarizes recent observational findings on cosmic ray anisotropies across a wide energy spectrum, discussing implications for magnetic fields and extragalactic origins, and highlighting new insights into cosmic ray sources and propagation.

Contribution

It provides a comprehensive overview of recent anisotropy measurements from TeV to trans-EeV energies and discusses their implications for cosmic ray origins and magnetic field environments.

Findings

Galactic magnetic fields influence cosmic ray anisotropies at TeV--PeV energies.

Extragalactic origin of ultra-high-energy cosmic rays has been observationally confirmed.

No definitive discrete sources of ultra-high-energy cosmic rays have been identified yet.

Abstract

Important observational results have been recently reported on the angular distributions of cosmic rays at all energies, calling into question the perception of cosmic rays a decade ago. These results together with their in-progress interpretations are summarised in this review paper, covering both large-scale and small-scale anisotropies from TeV energies to the highest ones. While the magnetic field in the Galaxy has long been considered as an external data imprinting a quasi-random walk to particles and thus shaping the angular distributions of Galactic cosmic rays through the induced average density gradient, the information encompassed in the angular distributions in the TeV--PeV energy range appear today as a promising tool to infer some properties of the local magnetic field environments. At the highest energies, the extragalactic origin of the particles has been recently determined observationally. While no discrete source of ultrahigh-energy cosmic rays has been identified so far, the noose is tightening around nearby extragalactic objects, and some prospects are discussed.