Observations at large zenith angles
Cherenkov telescope observations at zenith angles >70° are capable of providing large collection areas for high energy γ-induced air showers. In order to provide a full Monte Carlo simulation of the large zenith angle observations the air shower simulation code CORSIKA was modified to treat particles in a curved geometry. First results of studies with the stand alone telescope HEGRA CT1 are presented.

title: Recent Additions to the Extensive Air Shower Simulation Code CORSIKA
abstract: The Monte Carlo program CORSIKA simulates the evolution of extensive air showers in the atmosphere initiated by photons, hadrons or nuclei. Besides the already available 5 models DPMJET, HDPM, QGSJET, SIBYLL, and VENUS describing hadronic interactions at high energies we have added the new model NEXUS. Based on the universality hypothesis of the behavior of high energy interactions, NEXUS in its unified approach combines Gribov-Regge theory and perturbative QCD, including Reggeons, soft Pomerons, semi-hard Pomerons as a QCD-evolution of soft Pomerons, and parton-parton scattering. A further CORSIKA addition is the ‘curved’ option which allows a correct treatment of showers incident at large zenith angles > 70. At those angles a deviation from a planar atmosphere caused by the curvature of the Earth’s surface must be taken into account. The new extensions and features of CORSIKA are described.

title: Cherenkov light based measurement of extensive air showers around the knee with the HEGRA experiment
abstract: Data of the wide angle atmospheric Cherenkov light detector array AIROBICC and the scintillator matrix of the HEGRA air shower detector complex are combined to determine the energy spectrum and coarse composition of charged cosmic rays in the energy interval from 300 TeV to 10 PeV.

title: Energy spectrum and chemical composition of cosmic rays between 0.3 and 10 PeV determined from the Cherenkov-light and charged-particle distributions in air showers
abstract: Measurements of the lateral distribution of Cherenkov photons with the wide-angle atmospheric Cherenkov light detector array AIROBICC and of the charged particle lateral distribution with the scintillator matrix of the HEGRA air-shower detector complex in air showers are reported. They are used in conjunction to determine the energy spectrum and coarse chemical composition of charged cosmic rays in the energy interval from 0.3 PeV to 10 PeV. With the atmospheric shower-front sampling technique these detectors measure the electromagnetic component of an extensive air shower via the lateral density distribution of the shower particles and of the Cherenkov photons. The data are compared with events generated with the CORSIKA program package with the QGSJET hadronic-event generator. Consistency checks performed with primary energy-reconstruction methods based on different shower observables indicate satisfactory agreement between these extensive air shower simulations and the experimental data. This permits to derive results concerning the energy spectrum and composition of charged cosmic rays. The energy spectrum features a so called "knee" at

title: Rejection of the hypothesis that Mkn-501 TeV photons are pure Bose – Einstein condensates
abstract: The TeV energy spectrum of the Blazar type galaxy Mkn-501 as measured by the HEGRA air Cherenkov telescopes extends beyond 16 TeV and constitutes the most energetic photons observed from an extragalactic object. A fraction of the emitted spectrum is possibly absorbed in interactions with low energy photons of the diffuse extragalactic infrared radiation, which in turn offers the unique possibility to measure the diffuse infrared radiation density by exact TeV spectroscopy. The upper limit on the density of the extragalactic infrared radiation derived from the TeV observations imposes constraints on models of galaxy formation and stellar evolution. One of the recently published ideas to reduce the absorption of TeV photons is based upon the assumption Max-Planck-Institut für Kernphysik, Postfach 103980, D-69029 Heidelberg, Germany Max-Planck-Institut für Physik, Föhringer Ring 6, D-80805 München, Germany Universidad Complutense, Facultad de Ciencias F́isicas, Ciudad Universitaria, E-28040 Madrid, Spain Universität Hamburg, II. Institut für Experimentalphysik, Luruper Chaussee 149, D-22761 Hamburg, Germany Universität Kiel, Institut für Experimentelle und Angewandte Physik, Leibnizstraße 15-19, D-24118 Kiel, Germany Universität Wuppertal, Fachbereich Physik, Gaußstr.20, D-42097 Wuppertal, Germany Yerevan Physics Institute, Alikhanian Br. 2, 375036 Yerevan, Armenia On leave from Altai State University, Dimitrov Street 66, 656099 Barnaul, Russia Corresponding author: Dieter Horns Dieter.Horns@desy.de

title: Time Calibration of the Radio Air Shower Array LOPES
abstract: LOPES is a digitally read out antenna array consisting of 30 calibrated dipole antennas. It is located at the site of the KASCADE-Grande experiment at Forschungszentrum Karlsruhe and measures the radio emission of cosmic ray air showers in the frequency band from 40 to 80 MHz. LOPES is triggered by KASCADE and uses the KASCADE reconstruction of the shower axis as an input for the analysis of the radio pulses. Thereby LOPES works as an interferometer when the signal of all antennas is digitally merged to form a beam into the shower direction. To be sensitive to the coherence of the radio signal, a precise time calibration with an accuracy in the order of 1 ns is required. Thus, it is necessary to know the delay of each antenna which is time and frequency dependent. Several calibration measurements are performed to correct for this delay in the analysis: The group delay of every antenna is measured regularly (roughly once per year) by recording a test pulse which is emitted at a known time. Furthermore, the delay is monitored continuously by the so called phase calibration method: A beacon (a dipole antenna) emits continuously two sine waves at 63.5 MHz and 68.1 MHz. By that a variation of the delay can be detected in a subsequent analysis of the radio events as a change of the phase at these frequencies. Finally, the dispersion of the analog electronics has been measured to account for the frequency dependence of the delay.

title: Instruments and Methods for the Radio Detection of High Energy Cosmic Rays

title: Ultrahigh Energy Neutrinos at the Pierre Auger Observatory
abstract: The observation of ultrahigh energy neutrinos (UHE nu s) has become a priority in experimental astroparticle physics. UHE nu s can be detected with a variety of techniques. In particular, neutrinos can interact in the atmosphere (downward-going nu) or in the Earth crust (Earth-skimming nu), producing air showers that can be observed with arrays of detectors at the ground. With the surface detector array of the Pierre Auger Observatory we can detect these types of cascades. The distinguishing signature for neutrino events is the presence of very inclined showers produced close to the ground (i.e., after having traversed a large amount of atmosphere). In this work we review the procedure and criteria established to search for UHE nu s in the data collected with the ground array of the Pierre Auger Observatory. This includes Earth-skimming as well as downward-going neutrinos. No neutrino candidates have been found, which allows us to place competitive limits to the diffuse flux of UHE nu s in the EeV range and above.

title: Investigations of the radio signal of inclined showers with LOPES
abstract: We report in this paper on an analysis of 20 months of data taken with LOPES. LOPES is radio antenna array set-up in coincidence with the Grande array, both located at the Karlsruhe Institute of Technology, Germany. The data used in this analysis were taken with an antenna configuration composed of 30 inverted V-shape dipole antennas. We have restricted the analysis to a special selection of inclined showers—with zenith angle θ > 40 ∘ . These inclined showers are of particular interest because they are the events with the largest geomagnetic angles and are therefore suitable to test emission models based on geomagnetic effects.The reconstruction procedure of the emitted radio signal in EAS uses as one ingredient the frequency-dependent antenna gain pattern which is obtained from simulations. Effects of the applied antenna model in the calibration procedure of LOPES are studied. In particular, we have focused on one component of the antenna, a metal pedestal, which generates a resonance effect, a peak in the amplification pattern where it is the most affecting high zenith angles, i.e. inclined showers. In addition, polarization characteristics of inclined showers were studied in detail and compared with the features of more vertical showers for the two cases of antenna models, with and without the pedestal.