H. O. Klages

Impact of varying atmospheric profiles on extensive air shower observation: atmospheric density and primary mass reconstruction

Abstract 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 of primary cosmic rays. In this article, the impact of the atmospheric density profile on the reconstruction of the depth of maximum, as observed in fluorescence light measurements, is investigated. We consider in detail the atmospheric density profile and its time variations at the site of the southern Pierre Auger Observatory, using data that were obtained from meteorological radio soundings. Similar atmospheric effects are expected to be found also at other sites.

Spectral resolved measurement of the nitrogen fluorescence emissions in air induced by electrons

Abstract For the calorimetric determination of the primary energy of extensive air showers, measured by fluorescence telescopes, a precise knowledge of the conversion factor (fluorescence yield) between the deposited energy in the atmosphere and the number of emitted fluorescence photons is essential. The fluorescence yield depends on the pressure and the temperature of the air as well as on the water vapor concentration. Within the scope of this work the fluorescence yield for the eight strongest nitrogen emission bands between 300xa0nm and 400xa0nm has been measured using electrons from a 90Sr-source with energies between 250xa0keV and 2000xa0keV. Measurements have been performed in dry air, pure nitrogen, and a nitrogen–oxygen mixture at pressures ranging from 2xa0hPa to 990xa0hPa. Furthermore the influence of water vapor has been studied. A new approach for the parametrization of the fluorescence yield was used to analyze the data, leading to a consistent description of the fluorescence yield with a minimal set of parameters. The resulting absolute accuracies for the single nitrogen bands are in the order of 15%. In the investigated energy range, the fluorescence yield proved to be independent of the energy of the ionizing electrons.

Impact of varying atmospheric profiles on extensive air shower observation: Fluorescence light emission and energy reconstruction

Abstract Several experiments measure the fluorescence light produced by extensive air showers in the atmosphere. This light is converted into a longitudinal shower profile from which information on the primary energy and composition is derived. The fluorescence yield, as the conversion factor between light profile measured by EAS experiments and physical interpretation of showers, has been measured in several laboratory experiments. The results, however, differ considerably. In this article, a model calculation of the fluorescence emission from relevant band systems of nitrogen in dependence on wavelength and atmospheric conditions is presented. Different calculations are compared to each other in combination with varying input parameters. The predictions are compared with measurements and the altitude dependence of the fluorescence yield is discussed in detail.

Simulation of ultra-high energy photon propagation in the geomagnetic field ☆ ☆☆

The identification of primary photons or specifying stringent limits on the photon flux is of major importance for understanding the origin of ultra-high energy (UHE) cosmic rays. UHE photons can initiate particle cascades in the geomagnetic field, which leads to significant changes in the subsequent atmospheric shower development. We present a Monte Carlo program allowing detailed studies of conversion and cascading of UHE photons in the geomagnetic field. The program named PRESHOWER can be used both as an independent tool or together with a shower simulation code. With the stand-alone version of the code it is possible to investigate various properties of the particle cascade induced by UHE photons interacting in the Earth’s magnetic field before entering the Earth’s atmosphere. Combining this program with an extensive air shower simulation code such as CORSIKA offers the possibility of investigating signatures of photon-initiated showers. In particular, features can be studied that help to discern such showers from the ones induced by hadrons. As an illustration, calculations for the conditions of the southern part of the Pierre Auger Observatory are presented. Program summary