Search

This paper summarizes the status and the recent measurements from the Pierre Auger Observatory. The energy spectrum is described and its features discussed. We report searches for anisotropy of cosmic ray arrival directions on large scales and through correlation with catalogues of celestial objects. We also present the search for anisotropies in the data without the use of astronomical catalogues. The first measurement of the proton-air cross section around 10^{18} eV is discussed. Finally, the mass composition is addressed with measurements of the variation of the depth of shower maximum with energy and with the muon density at ground., Comment: Prepared for a special topical issue of Advances in Space Research (ASR) entitled "Cosmic Ray Origins: Viktor Hess Centennial Anniversary". Presented at COSPAR 2012, Mysore, India

We report a measurement of the cosmic ray energy spectrum based on a large amount of data collected by the Pierre Auger Observatory. This measurement combines data from the fluorescence (FD) and surface (SD) detectors of the Observatory and does not rely on detailed numerical simulation or any assumption about the chemical composition. The energy calibration of the observables, which exploits the correlation of surface detector data with fluorescence measurements in hybrid events, is presented in detail. Besides presenting statistical uncertainties, we address the impact of systematic uncertainties. We also summarize the combined energy spectrum obtained when hybrid data are used to extend the spectrum to lower energies.

The Pierre Auger Observatory studies the most energetic cosmic rays arriving at Earth, those with energies from 1017 eV up to 1020 eV and beyond. In continuous operation since 2004, the Observatory employs two complementary detection techniques for measuring air showers induced by those extremely energetic particles. For the past few years new detectors and techniques are being added in order to augment the sensitivity of the measurements. Data accumulated in ten years have led to major advances in our knowledge of the origin and nature of cosmic rays. We present a summary of the latest results for the spectrum of cosmic rays, their arrival directions and composition, as well as the challenges for the future operation of the Observatory.

The Pierre Auger Observatory in Argentina is the largest cosmic ray detector array ever built. Although the construction was completed in 2008, the Observatory has been taking data continuously since January 2004. Its main goal is to measure ultra high energy cosmic rays (UHECRs, energy above 10 18 eV) with unprecedented statistics and precision. Measurements of the energy spectrum, chemical composition (including neutrinos and photons) and arrival directions of UHECRs can provide hints for understanding their origin, propagation and interactions. The fluorescence detector of the Pierre Auger Observatory measures the atmospheric depth, X max , where the longitudinal profile of a high energy air shower reaches its maximum. This is sensitive to the nuclear mass composition of the cosmic ray and to the characteristics of the hadronic interactions at very high energy. Due to its hybrid design, the Pierre Auger Observatory also provides independent experimental observables obtained from the surface detector for the study of the shower development. A selection of the Pierre Auger Observatory results on the study of the UHECRs will be presented, focusing on composition results. In particular, the measurements and the different roles of the observables with respect to mass composition will be discussed.