C. Timmermans

The Fluorescence Detector of the Pierre Auger Observatory

The Pierre Auger Observatory is a hybrid detector for ultra-high energy cosmic rays. It combines a surface array to measure secondary particles at ground level together with a fluorescence detector to measure the development of air showers in the atmosphere above the array. The fluorescence detector comprises 24 large telescopes specialized for measuring the nitrogen fluorescence caused by charged particles of cosmic ray air showers. In this paper we describe the components of the fluorescence detector including its optical system, the design of the camera, the electronics, and the systems for relative and absolute calibration. We also discuss the operation and the monitoring of the detector. Finally, we evaluate the detector performance and precision of shower reconstructions.

Constraints on the origin of cosmic rays above 10(18) eV from large-scale anisotropy searches in data of the Pierre Auger Observatory

A thorough search for large-scale anisotropies in the distribution of arrival directions of cosmic rays detected above 10(18) eV at the Pierre Auger Observatory is reported. For the first time, these large-scale anisotropy searches are performed as a function of both the right ascension and the declination and expressed in terms of dipole and quadrupole moments. Within the systematic uncertainties, no significant deviation from isotropy is revealed. Upper limits on dipole and quadrupole amplitudes are derived under the hypothesis that any cosmic ray anisotropy is dominated by such moments in this energy range. These upper limits provide constraints on the production of cosmic rays above 10(18) eV, since they allow us to challenge an origin from stationary galactic sources densely distributed in the galactic disk and emitting predominantly light particles in all directions.A thorough search for large scale anisotropies in the distribution of arrival directions of cosmic rays detected above 1018 eV at the Pierre Auger Observatory is reported. For the first time, these large scale anisotropy searches are performed as a function of both the right ascension and the declination and expressed in terms of dipole and quadrupole moments. Within the systematic uncertainties, no significant deviation from isotropy is revealed. Upper limits on dipole and quadrupole amplitudes are derived under the hypothesis that any cosmic ray anisotropy is dominated by such moments in this energy range. These upper limits provide constraints on the production of cosmic rays above 1018 eV, since they allow us to challenge an origin from stationary galactic sources densely distributed in the galactic disk and emitting predominantly light particles in all directions. Subject headings: astroparticle physics — cosmic rays The large scale distribution of arrival directions of Ultra-High Energy Cosmic Rays (UHECRs) as a function of the energy is a key observable to provide further understanding of their origin. Above ≃ 0.25 EeV, the most stringent bounds ever obtained on the dipole component in the equatorial plane were recently reported, being below 2% at 99% C.L. for EeV energies (Auger Collaboration 2011a). Such a sensitivity provides some constraints upon scenarios in which dipolar anisotropies could be imprinted in the distribution of arrival directions as the result of the escape of UHECRs from the Galaxy up to the ankle energy (Ptuskin et al. 1993; Candia et al. 2003; Giacinti et al. 2012). On the other hand, if UHECRs above 1 EeV have already a predominant extragalactic origin (Hillas 1967; Blumenthal 1970; Berezinsky et al. 2006; Berezinsky et al. 2004), their angular distribution is expected to be isotropic to a high level. Thus, the study of large scale anisotropies at EeV energies would help in establishing whether the origin of UHECRs is galactic or extragalactic in this energy range. The upper limits aforementioned are based on first harmonic analyses of the right ascension distributions in several energy ranges. The analyses benefit from the almost uniform directional exposure in right ascension of any ground based observatory operating with high duty cycle, but are not sensitive to a dipole component along the Earth rotation axis. In contrast, using the large amount of data collected by the surface detector array of the Pierre Auger Observatory, we report in this letter on searches for dipole and quadrupole patterns significantly standing out above the background noise whose components are functions of both the right ascension and the declination (a detailed description of the present analysis can be found in (Auger Collaboration 2012)).

Bounds on the density of sources of ultra-high energy cosmic rays from the Pierre Auger Observatory

We derive lower bounds on the density of sources of ultra-high energy cosmic rays from the lack of significant clustering in the arrival directions of the highest energy events detected at the Pierre Auger Observatory. The density of uniformly distributed sources of equal intrinsic intensity was found to be larger than similar to (0.06 - 5) x 10(-4) Mpc(-3) at 95% CL, depending on the magnitude of the magnetic defections. Similar bounds, in the range (0.2 - 7) x 10(-4) Mpc(-3), were obtained for sources following the local matter distribution.We present constraints on the density of sources obtained by analyzing the clustering (or absence of clustering) of the arrival directions of ultra-high energy cosmic rays detected at the Pierre Auger Observatory. We consider bounds for isotropically distributed sources and for sources distributed according to the 2MRS catalog.

Interpretation of the depths of maximum of extensive air showers measured by the Pierre Auger Observatory

To interpret the mean depth of cosmic ray air shower maximum and its dispersion, we parametrize those two observables as functions of the first two moments of the

Anisotropy and chemical composition of ultra-high energy cosmic rays using arrival directions measured by the Pierre Auger Observatory

\ln A

Test results of the L3 precision muon detector

distribution. We examine the goodness of this simple method through simulations of test mass distributions. The application of the parameterization to Pierre Auger Observatory data allows one to study the energy dependence of the mean

Muon detection in the L3 experiment at LEP

\ln A

Enhancements to the Southern Pierre Auger Observatory

and of its variance under the assumption of selected hadronic interaction models. We discuss possible implications of these dependences in term of interaction models and astrophysical cosmic ray sources.To interpret the mean depth of cosmic ray air shower maximum and its dispersion, we parametrize those two observables as functions of the first two moments of the ln A distribution. We examine the goodness of this simple method through simulations of test mass distributions. The application of the parameterization to Pierre Auger Observatory data allows one to study the energy dependence of the mean ln A and of its variance under the assumption of selected hadronic interaction models. We discuss possible implications of these dependences in term of interaction models and astrophysical cosmic ray sources.

Study of θ-inclined tracks in L3 muon chambers

The Pierre Auger Collaboration has reported. evidence for anisotropy in the distribution of arrival directions of the cosmic rays with energies E > E(th) = 5.5 x 10(19) eV. These show a correlation with the distribution of nearby extragalactic objects, including an apparent excess around the direction of Centaurus A. If the particles responsible for these excesses at E > E(th) are heavy nuclei with charge Z, the proton component of the sources should lead to excesses in the same regions at energies E/Z. We here report the lack of anisotropies in these directions at energies above E(th)/Z (for illustrative values of Z = 6, 13, 26). If the anisotropies above E(th) are due to nuclei with charge Z, and under reasonable assumptions about the acceleration process, these observations imply stringent constraints on the allowed proton fraction at the lower energies.

Spectral calibration of the fluorescence telescopes of the Pierre Auger Observatory

Abstract The L3 detector is designed to measure the muon momentum with a 2% resolution at p = 45 GeV/c. We discuss here the systems we developed to reach the required accuracy and control the mechanical alignment at running time. We also report on the test done on the muon spectrometer with UV lasers and cosmic rays.