AstroParticle Physics at the Highest Energies

TL;DR

Recent advancements in cosmic ray, gamma ray, and neutrino observatories are enhancing our understanding of ultra-high-energy cosmic phenomena, revealing new sources, anisotropies, and composition changes, yet the origin of the highest energy particles remains elusive.

Contribution

This paper reviews recent progress in high-energy astrophysics, highlighting new observational data and the challenges in identifying cosmic ray sources at ultrahigh energies.

Findings

Increased number of gamma-ray sources detected.

Confirmation of spectral features like the ankle and GZK cutoff.

Evidence of anisotropies in cosmic ray arrival directions.

Abstract

Recent international efforts have brought us closer to unveiling the century old mystery of the origin of cosmic rays. Cosmic ray, gamma ray, and neutrino observatories are reaching the necessary sensitivity to study the highest energy cosmic accelerators and to begin the use of cosmic particles to study particle interactions above laboratory energies. The number of known gamma-ray sources has increased by orders of magnitude. Possible cosmic ray sources have narrowed down with the confirmation of an ankle and the GZK-like spectral feature at the highest energies. Anisotropies in the distribution of arrival directions of cosmic rays at intermediate energies show a complex local neighborhood of the Galaxy. At the highest energies the dawn of particle astronomy is still challenging while composition related measurements point to a change in the composition or the interaction of cosmic rays at ultrahigh energies. A clear resolution of the ultrahigh energy mystery calls for a significant increase in statistics of cosmic ray and neutrino observations.