Parametrization of the angular distribution of Cherenkov light in air showers

The Cherenkov light produced in air showers largely contributes to the signal observed in ground-based gamma-ray and cosmic-ray observatories. Yet, no description of this phenomenon is available covering both regions of small and large angles to the shower axis. To fill this gap, a parametrization of the angular distribution of Cherenkov photons is performed in terms of a physically-motivated parametric function. Model parameters are constrained using simulated gamma-ray and proton showers with energies in the TeV to EeV region. As a result, a new parametrization is obtained that improves the precision of previous works. Results presented here can be used in the reconstruction of showers with imaging Cherenkov telescopes as well as in the reconstruction of shower profiles with fluorescence detectors.

Muon Measurements with IceTop

We present the measurement of the density of GeV muons in near-vertical air showers by the IceTop array at the South Pole. The muon density is measured at 600 m and 800 m lateral distance from the shower axis in air showers between 1 PeV and 100 PeV. This result can be used to constrain hadronic interaction models by comparing it with the outcome of Monte Carlo simulations. We show that some models do not produce muon densities in agreement with this result unless an unphysical composition of the primary cosmic ray flux is assumed.

Latest results on the analysis of the radio frequency spectrum emitted by high energy air showers with LOFAR

The LOw Frequency ARay (LOFAR) is a multi-purpose radio antenna array aimed to detect radio signals in the frequency range 10 - 240 MHz, covering a largesurface in Northern Europe with a higher density in the Netherlands. Analytical calculations and simulation studies performed in the 2000s indicate a dependence of the radio frequency spectrum on cosmic-ray characteristics. The high number density of radio antennas at the LOFAR core allows to characterise the observed cascade in a detailed way. The radio signal emitted by air showers in the atmosphere has been studied accurately in the 30 - 80 MHz frequency range. The analysis has been conducted on simulated eventsand on real data detected by LOFAR since 2011. The final aim of this study is to find an independent method to infer information of primary cosmic rays for improving the reconstruction of primary particle parameters. Results show a strong dependence of the frequency spectrum on the distance to the shower axis for both real data and simulations. Furthermore, results show that this method is very sensitive to the precision in reconstructing the position of the shower axis at ground, and to different antenna calibration procedures. A correlation between the frequency spectrum and geometrical distance to the shower maximum development Xmax has also been investigated.

MUONS WITH Eth ≥ 1 GEV AND MASS COMPOSITION IN THE ENERGY RANGE 1018 - 1020EV OBSERVED BY YAKUTSK EAS ARRAY

The ratio of the muon flux density to charged particle flux density at distances of 300 and 600 m from the shower axis (ρμ(300)/ρ s (300) and ρμ(600)/ρ s (600)) is measured. In addition, the energy dependence of ρμ(1000) is analysed for showers with energies above 1018 eV. A comparison between the experimental data and calculations performed with the QGSJET model is given for the cases of primary proton, iron nucleus and gamma-ray. We conclude that the showers with E0 ≥ 3 × 1018 eV can be formed by light nuclei with a pronounced fraction of protons and helium nuclei. It is not excluded however that a small part of showers with energies above 1019 eV could be initiated by primary gamma-rays.

An Analysis of Cosmic Ray Air Showers for the Determination of Shower Age

A sample of 8651 air showers in the size range 104 . 3_106 . 2 has been analysed to determine the distribution of the measured age in terms of (i) the number of showers in a specified size range, and (ii) the radial distances in individual showers. It is shown that the radial age distribution in an individual shower leads to an average shower age approximately the same as the prediction of the electron-photon cascade theory. The other results include a study of the variation of (i) shower age, as measured by the x2-minimisation technique, with shower size of vertically incident showers, and (ii) the measured electron density at any point with its radial distance from the shower axis, as a function of the age of a large shower group with very small spread in size. A comparison of similar measurements with relevant theory is also included.