The Fluorescence Detector of the Pierre Auger Observatory - A Calorimeter for UHECR

The Pierre Auger Observatory is a hybrid detector for ultrahigh energy cosmic rays (UHECR) with energies above 10$^{18.5}$ eV. Currently the first part of the Observatory nears completion in the southern hemisphere in Argentina. One detection technique uses over 1600 water Cherenkov tanks at ground where samples of secondary particles of extensive air showers (EAS) are detected. The second technique is a calorimetric measurement of the energy deposited by EAS in the atmosphere. Charged secondary particles of EAS lose part of their energy in the atmosphere via ionization. The deposited energy is converted into excitation of molecules of the air and afterwards partly emitted as fluorescence light mainly from nitrogen in the wavelength region between 300 and 400 nm. This light is observed with 24 fluorescence telescopes in 4 stations placed at the boundary of the surface array. This setup provides a combined measurement of the longitudinal shower development and the lateral particle distribution at ground of the same event. Details on the fluorescence technique and the necessary atmospheric monitoring will be presented, as well as first physics results on UHECR.Comment: Proceedings of XII International Conference on Calorimetry in High Energy Physics (CALOR06), Chicago, USA, 2006 submitted to AIP proceeding

Altitude dependence of fluorescence light emission by extensive air showers

Fluorescence light is induced by extensive air showers while developing in the Earth's atmosphere. The number of emitted fluorescence photons depends on the conditions of the air and on the energy deposited by the shower particles at every stage of the development. In a previous model calculation, the pressure and temperature dependences of the fluorescence yield have been studied on the basis of kinetic gas theory, assuming temperature-independent molecular collision cross-sections. In this work we investigate the importance of temperature-dependent collision cross-sections and of water vapour quenching on the expected fluorescence yield. The calculations will be applied to simulated air showers while using actual atmospheric profiles to estimate the influence on the reconstructed energy of extensive air showers.Comment: 8 pages, 18 figures, to be published in Proc. 5th Fluorescence Workshop, El Escorial - Madrid, Sept. 200

The Balloon-the-Shower programme of the Pierre Auger Observatory

Abstract. The southern part of the Pierre Auger Observatory in Argentina investigates cosmic rays with energies above about 5·10 17 eV. High-energy events which have been recorded with both detector components, surface water Cherenkov tanks and fluorescence telescopes, are crucial for the energy calibration of the entire detector system. Using this method, the energy reconstruction of extensive air showers relies on a proper fluorescence light reconstruction which depends on the knowledge of atmospheric conditions like pressure, temperature and water vapour. These properties of the atmosphere vary with altitude and in time. Therefore, a dedicated monitoring programme has operated since March 2009 to measure an actual atmospheric profile with meteorological radio soundings shortly after the detection of a high-energy air shower with E 0 > 2·10 19 eV. We will present the technical implementation of this programme as well as a reconstruction analysis using the data obtained. The reconstructed primary energy of air showers and the position of the shower maximum are compared with those results using either monthly models for the local atmospheric conditions or global meteorological models

The Balloon-the-Shower programme of the Pierre Auger Observatory

Abstract. The southern part of the Pierre Auger Observatory in Argentina investigates cosmic rays with energies above about 5·10 17 eV. High-energy events which have been recorded with both detector components, surface water Cherenkov tanks and fluorescence telescopes, are crucial for the energy calibration of the entire detector system. Using this method, the energy reconstruction of extensive air showers relies on a proper fluorescence light reconstruction which depends on the knowledge of atmospheric conditions like pressure, temperature and water vapour. These properties of the atmosphere vary with altitude and in time. Therefore, a dedicated monitoring programme has operated since March 2009 to measure an actual atmospheric profile with meteorological radio soundings shortly after the detection of a high-energy air shower with E 0 > 2·10 19 eV. We will present the technical implementation of this programme as well as a reconstruction analysis using the data obtained. The reconstructed primary energy of air showers and the position of the shower maximum are compared with those results using either monthly models for the local atmospheric conditions or global meteorological models

Nitrogen fluorescence in air for observing extensive air showers

Extensive air showers initiate the fluorescence emissions from nitrogen molecules in air. The UV-light is emitted isotropically and can be used for observing the longitudinal development of extensive air showers in the atmosphere over tenth of kilometers. This measurement technique is well-established since it is exploited for many decades by several cosmic ray experiments. However, a fundamental aspect of the air shower analyses is the description of the fluorescence emission in dependence on varying atmospheric conditions. Different fluorescence yields affect directly the energy scaling of air shower reconstruction. In order to explore the various details of the nitrogen fluorescence emission in air, a few experimental groups have been performing dedicated measurements over the last decade. Most of the measurements are now finished. These experimental groups have been discussing their techniques and results in a series of Air Fluorescence Workshops commenced in 2002. At the 8$^{\rm{th}}$ Air Fluorescence Workshop 2011, it was suggested to develop a common way of describing the nitrogen fluorescence for application to air shower observations. Here, first analyses for a common treatment of the major dependences of the emission procedure are presented. Aspects like the contributions at different wavelengths, the dependence on pressure as it is decreasing with increasing altitude in the atmosphere, the temperature dependence, in particular that of the collisional cross sections between molecules involved, and the collisional de-excitation by water vapor are discussed.Comment: 12 pages, 17 figures, 2 tables, International Symposium on Future Directions in UHECR Physics, 13-16 February 2012, CERN, Geneva (Switzerland); the updated version corrects for a typo in Eq. (1

Atmospheric Calorimetry above 1019^{19} eV: Shooting Lasers at the Pierre Auger Cosmic-Ray Observatory

The Pierre Auger Cosmic-Ray Observatory uses the earth's atmosphere as a calorimeter to measure extensive air-showers created by particles of astrophysical origin. Some of these particles carry joules of energy. At these extreme energies, test beams are not available in the conventional sense. Yet understanding the energy response of the observatory is important. For example, the propagation distance of the highest energy cosmic-rays through the cosmic microwave background radiation (CMBR) is predicted to be strong function of energy. This paper will discuss recently reported results from the observatory and the use of calibrated pulsed UV laser "test-beams" that simulate the optical signatures of ultra-high energy cosmic rays. The status of the much larger 200,000 km$^3$ companion detector planned for the northern hemisphere will also be outlined.Comment: 6 pages, 11 figures XIII International Conference on Calorimetry in High Energy Physic

Description of Atmospheric Conditions at the Pierre Auger Observatory Using Meteorological Measurements and Models

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 sophisticated network of atmospheric monitoring devices has been conceived. Part of this monitoring was a weather balloon program to measure atmospheric state variables above the Observatory. To use the data in reconstructions of air showers, monthly models have been constructed. Scheduled balloon launches were abandoned and replaced with launches triggered by high-energetic air showers as part of a rapid monitoring system. Currently, the balloon launch program is halted and atmospheric data from numerical weather prediction models are used. A description of the balloon measurements, the monthly models as well as the data from the numerical weather prediction are presented

Atmospheric Profiles at the Southern Pierre Auger Observatory and their Relevance to Air Shower Measurement

The dependence of atmospheric conditions on altitude and time have to be known at the site of an air shower experiment for accurate reconstruction of extensive air showers and their simulations. The height-profile of atmospheric depth is of particular interest as it enters directly into the reconstruction of longitudinal shower development and of the primary energy and mass of cosmic rays. For the southern part of the Auger Observatory, the atmosphere has been investigated in a number of campaigns with meteorological radio soundings and with continuous measurements of ground-based weather stations. Focussing on atmospheric depth and temperature profiles, temporal variations are described and monthly profiles are developed. Uncertainties of the monthly atmospheres that are currently applied in the Auger reconstruction are discussed.Comment: To be published in Proceedings of 29th International Cosmic Ray Conference (ICRC) 2005, Pune, Indi