Ultra High-Energy Cosmic Ray Observations

TL;DR

In 2007, significant progress was made in understanding ultra high-energy cosmic rays, including observing flux suppression consistent with the GZK effect and identifying correlations with nearby active galactic nuclei, marking a breakthrough in cosmic ray astronomy.

Contribution

This paper reports the first observational evidence linking ultra high-energy cosmic rays to nearby active galactic nuclei, advancing the field towards cosmic ray source identification.

Findings

Flux suppression consistent with GZK effect observed

Correlations between cosmic rays and nearby AGN detected

Progress towards ultra high-energy cosmic ray astronomy

Abstract

The year 2007 has furnished us with outstanding results about the origin of the most energetic cosmic rays: a flux suppression as expected from the GZK-effect has been observed in the data of the HiRes and Auger experiments and correlations between the positions of nearby AGN and the arrival directions of trans-GZK events have been observed by the Pierre Auger Observatory. The latter finding marks the beginning of ultra high-energy cosmic ray astronomy and is considered a major breakthrough starting to shed first light onto the sources of the most extreme particles in nature. This report summarizes those observations and includes other major advances of the field, mostly presented at the 30th International Cosmic Ray Conference held in Merida, Mexico, in July 2007. With increasing statistics becoming available from current and even terminated experiments, systematic differences amongst different experiments and techniques can be studied in detail which is hoped to improve our understanding of experimental techniques and their limitations.