Energy spectrum of ultra high energy cosmic rays

TL;DR

This paper reports on the construction and initial measurements of the Pierre Auger Observatory's southern site, confirming flux suppression at ultra-high energies and extending the cosmic ray spectrum to lower energies.

Contribution

It provides the first combined measurements of cosmic ray flux using surface and fluorescence detectors, revealing flux suppression and spectral features at ultra-high energies.

Findings

Flux suppression at energies above 1 EeV with 6 sigma significance

Extended energy spectrum to lower energies using fluorescence data

First combined flux measurements from surface and fluorescence detectors

Abstract

The construction of the southern site of the Pierre Auger Observatory is almost completed. Three independent measurements of the flux of the cosmic rays with energies larger than 1 EeV have been performed during the construction phase. The surface detector data collected until August 2007 have been used to establish a flux suppression at the highest energies with a 6 sigma significance. The observations of cosmic rays by the fluorescence detector allowed the extension of the energy spectrum to lower energies, where the efficiency of the surface detector is less than 100% and a change in the spectral index is expected.