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Selected results of department 16

Introducing the CTA concept

The Cherenkov Telescope Array (CTA) is an upcoming observatory for very high-energy gamma rays. CTA has ambitious scientific goals, for which it is required to achieve a full-sky coverage, to improve the sensitivity by about an order of magnitude and to span about four orders of energy, from a few tens of GeV to above 100 TeV with better angular and energy resolution than the existing VHE gamma-ray observatories. The paper introduces general concepts of this project.

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Measurement of the depth of maximum of extensive air showers above 1 EeV

The paper is based on the long-period data acquired by the Pierre Auger Observatory. The presented results concern the analysis of the unique data set encompassing 4000 atmospheric air showers detected simultaneously by the surface and fluorescence detectors, while the observed parameter was the depth of shower maximum estimated from the fluorescence detector measurement. A transition from light to heavy elements with increasing energy is observed in the spectrum of incoming primary cosmic rays.

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Search for microwave emission from ultrahigh energy cosmic rays

The most precise method of high energy cosmic ray detection - the fluorescence technique - has the drawback of being usable only during clear moonless nights amounting only to about 15% of the time. This paper presents an effort to develop an alternative technique independent of daylight or weather conditions. A telescope detecting cosmic ray air showers in a microwave range was realized at the University of Chicago. The paper presents experiment MIDAS using this technique, first measurements and results.

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The rapid atmospheric monitoring system of the Pierre Auger Observatory

The atmospheric monitoring program of the Pierre Auger Observatory allows for a targeted measurement of atmospheric conditions shortly after the detection of air showers of special interest. This helps especially to improve the fluorescence detector reconstruction of such events. The paper reports on the implementation of the rapid monitoring program and its status. The rapid monitoring program is found to have a potential for supporting dedicated physics analyses beyond the standard event reconstruction.

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Muons in air showers at the Pierre Auger Observatory: Measurement of atmospheric production depth

Phys. Rev. D 90 (2014) 012012(1)–012012(15), doi: 10.1103/PhysRevD.90.012012

The surface detector array of the Pierre Auger Observatory provides information about the longitudinal development of the muonic component of extensive air showers. Using the timing information from the flash analog-to-digital converter traces of surface detectors far from the shower core, it is possible to reconstruct a muon production depth distribution. The whole text »

A study of the effect of molecular and aerosol conditions in the atmosphere on air fluorescence measurements at the Pierre Auger Observatory

The atmospheric data are used extensively in the reconstruction of air showers at the Pierre Auger Observatory, and are particularly important for the correct determination of shower energies and depths of the shower maximum from the fluorescence detector measurements. This paper contains a summary of the molecular and aerosol conditions at the Observatory site and includes a discussion about the impact of these measurements on the air shower reconstruction.

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Precise measurement of the absolute fluorescence yield of the 337 nm band in atmospheric gases

Absolute fluorescence yield is a crucial value used for energy reconstruction by fluorescence detectors of cosmic rays. This paper is presenting a result of ten years of comprehensive studies of the air fluorescence process by the AirFly group. The total uncertainty of the absolute fluorescence yield, which propagates into the uncertainty of the energy reconstruction of high-energy-cosmic-ray detectors, has been lowered from 15% to 4%.

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Anisotropy of cosmic rays at ultra-high energies

The observed anisotropy of arrival directions of incoming cosmic ray particles with energy above 6 . 1019 eV is one of the most important results of the Pierre Auger Observatory. Such particles are very rare and during 50 years of their measurement at different observatories only few tens of them were detected. Because of their extremely large energy, that is many orders of magnitude larger than what humans can produce in laboratories, their existence is very puzzling and no existing astrophysical theory can fully explain their production. The whole text »

The fluorescence detector of the Pierre Auger Observatory

This extensive paper concisely describes all components of the fluorescence detector of the Pierre Auger Observatory including its optical system, the design of the camera, the electronics and the systems for relative and absolute calibrations. The operation and the monitoring of the detector are discussed and the detector performance and precision of shower reconstruction is evaluated. The paper is the major reference to the currently  largest system of fluorescence telescopes ever built. The whole text »