S. Grebe

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)).

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

Enhancements to the Southern Pierre Auger Observatory

\ln A

Limit on the diffuse flux of ultrahigh energy tau neutrinos with the surface detector of the Pierre Auger Observatory

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

Publisher's Note: Muons in air showers at the Pierre Auger Observatory: Mean number in highly inclined events [Phys. Rev. D, 91 , 032003 (2015)]

\ln A

The rapid atmospheric monitoring system of the 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.

Publisher's Note: Muons in air showers at the Pierre Auger Observatory: Measurement of atmospheric production depth [Phys. Rev. D \textbf{90} , 012012 (2014)]

The southern Pierre Auger Observatory has been detecting cosmic rays above 1018eV since 2004, exploiting a hybrid air shower detection technique, with 1660 water Cherenkov detectors together with 24 air fluorescence telescopes on a 3000 km2 site. As low energy enhancements to the observatory, 3 additional telescopes with elevated fields of view were built (HEAT). The detector density was increased in the HEAT fields of view by a factor of four in an area of about 25 km2. This setup enables unbiased hybrid data taking above 1017eV. The infilled area is also being equipped with large underground scintillator muon detectors (AMIGA). Finally, a prototype array of radio antenna stations (AERA), working from 30 to 80 MHz, has been installed in a part of the infill. Properties and status of AMIGA, HEAT, and AERA are presented.The southern Pierre Auger Observatory was designed to detect ultrahig h energy cosmic rays above 10 eV with high accuracy exploiting a hybrid detection technique. A surface arra y of 1660 water Cherenkov detectors on a 1500 m triangular grid covers an area of 3000 km. The atmosphere above the array is viewed by 24 wide angle telescopes. These telescopes observe the faint fluorescence light of the extensive air showers at dark moonless nights, i.e. with a duty cycle of about 15 %. As an enhancement to this baseline design o f the Auger Observatory three additional telescopes with elevated field of view were built and now constitute HEAT, the h igh-elevation Auger telescopes. These telescopes are similar to the 24 other fluorescence telescopes (FD) but c an be tilted by29 degrees upward. They cover an elevation range from30 to 58 degrees above horizon to enable the unbiased detection of nearby low en ergy air showers. Especially in combination with the detector information from an infill array of w ater tanks on a750m grid close to the HEAT site the energy range of high quality hybrid air shower measuremen ts is extended down to below 10 eV. HEAT is fully commissioned and is taking data continuously since September 2009. The status and prospects of HEAT are discussed and first (preliminary) data are presented.