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Measurements of air showers are accumulating at an increasing rate while construction proceeds at the Pierre Auger Observatory. Although the southern site is only half complete, the cumulative exposure is already similar to those achieved…
We describe the analysis of longitudinal air shower profiles as measured by the fluorescence detectors of the Pierre Auger Observatory and present the measurement of the depth of maximum of extensive air showers, Xmax, with energies >10^18…
Air fluorescence measurements of cosmic ray energy must be corrected for attenuation of the atmosphere. In this paper we show that the air-showers themselves can yield a measurement of the aerosol attenuation in terms of optical depth,…
We report on studies of the composition of ultra high energy cosmic rays with the Pierre Auger Observatory. The detection of longitudinal air shower profiles with the fluorescence detector is described and the measurement of the average…
The Pierre Auger Observatory is a detector for ultra-high energy cosmic rays. It consists of a surface array to measure secondary particles at ground level and a fluorescence detector to measure the development of air showers in the…
The goal of the Pierre Auger Observatory is to determine the still unknown nature and origin of ultra-high energy cosmic rays. The study of these elusive particles probes astrophysical sites of particle acceleration as well as fundamental…
The world's largest cosmic-ray detector is nearing completion in the remote Pampas of Argentina. This instrument measures extensive air-showers with energies from ${10^{18}-10^{20}}$ eV and beyond. A surface detector array of area 3000…
The absolute calibration of an air fluorescence detector (FD) is an important element in correctly determining the energy of detected cosmic rays. The absolute calibration relates the flux of photons of a given wavelength at the detector…
The Pierre Auger Observatory is a hybrid detector designed to observe and study ultra-high-energy particles of extraterrestrial origin. With its 27 fluorescence telescopes and over 1600 autonomously operating water-Cherenkov detectors…
The High Elevation Auger Telescopes (HEAT) are three tiltable fluorescence telescopes which represent a low energy enhancement of the fluorescence telescope system of the southern site of the Pierre Auger Observatory in Argentina. The…
Atmospheric conditions at the site of a cosmic ray observatory must be known well for reconstructing observed extensive air showers, especially when measured using the fluorescence technique. For the Pierre Auger Observatory, a…
The Pierre Auger Observatory is the most sensitive instrument to detect photons with energies above $10^{17}$ eV. It measures extensive air showers generated by ultra high energy cosmic rays using a hybrid technique that exploits the…
The Pierre Auger Observatory aims to determine the nature and origin of the ultra-high energy cosmic rays (UHECR). The Auger hybrid detector combines fluorescence observations of extended air showers, initiated in the atmosphere by these…
The Pierre Auger Observatory is the world's largest detector of ultra--high energy cosmic rays (UHECRs). It uses an array of fluorescence telescopes and particle detectors at the ground to obtain detailed measurements of the energy…
The Pierre Auger Observatory is making significant contributions towards understanding the nature and origin of ultra-high energy cosmic rays. One of its main challenges is the monitoring of the atmosphere, both in terms of its state…
The Pierre Auger Collaboration is exploring the potential of radio-detection techniques to measure the extensive air showers. The main advantage of these setups is the possibility to cover a large area with no atmospheric attenuation and…
The longitudinal profile of extensive air showers is sensitive to the energy and type/mass of the primary particle. One of its characteristics, the atmospheric depth of shower maximum, is often used to reconstruct the elemental composition…
The Fluorescence Detector of the Pierre Auger Observatory measures the atmospheric depth, $X_{max}$, where the longitudinal profile of the high energy air showers reaches its maximum. This is sensitive to the nuclear mass composition of the…
The average profiles of cosmic ray shower development as a function of atmospheric depth are measured for the first time with the Fluorescence Detectors at the Pierre Auger Observatory. The profile shapes are well reproduced by the…
The determination of the primary energy of extensive air showers using the fluorescence detection technique requires an estimation of the energy carried away by particles that do not deposit all their energy in the atmosphere. This…