T. Asch

Trigger and aperture of the surface detector array of the Pierre Auger Observatory

The surface detector array of the Pierre Auger Observatory consists of 1600 water-Cherenkov detectors, for the study of extensive air showers (EAS) generated by ultra-high-energy cosmic rays. We describe the trigger hierarchy, from the identification of candidate showers at the level of a single detector, amongst a large background (mainly random single cosmic ray muons), up to the selection of real events and the rejection of random coincidences. Such trigger makes the surface detector array fully efficient for the detection of EAS with energy above 3 x 10(18) eV, for all zenith angles between 0 degrees and 60 degrees, independently of the position of the impact point and of the mass of the primary particle. In these range of energies and angles, the exposure of the surface array can be determined purely on the basis of the geometrical acceptance

Lateral distribution of the radio signal in extensive air showers measured with LOPES

The antenna array LOPES is set up at the location of the KASCADE-Grande extensive air shower experiment in Karlsruhe, Germany and aims to measure and investigate radio pulses from extensive air showers. The coincident measurements allow us to reconstruct the electric field strength at observation level in dependence of general EAS parameters. In the present work, the lateral distribution of the radio signal in air showers is studied in detail. It is found that the lateral distributions of the electric field strengths in individual EAS can be described by an exponential function. For about 20% of the events a flattening towards the shower axis is observed, preferentially for showers with large inclination angle. The estimated scale parameters R0, describing the slope of the lateral profiles range between 100 and 200 m. No evidence for a direct correlation of R0 with shower parameters like azimuth angle, geomagnetic angle, or primary energy can be found. This indicates that the lateral profile is an intrinsic property of the radio emission during the shower development which makes the radio detection technique suitable for large scale applications.

Frequency spectra of cosmic ray air shower radio emission measured with LOPES

Aims. We wish to study the spectral dependence of the radio emission from cosmic-ray air showers around 100 PeV (10 17 eV). Methods. We observe short radio pulses in a broad frequency band with the dipole-interferometer LOPES (LOFAR Prototype Station), which is triggered by a particle detector array named Karlsruhe Shower Core and Array Detector (KASCADE). LOFAR is the Low Frequency Array. For this analysis, 23 strong air shower events are selected using parameters from KASCADE. The radio data are digitally beam-formed before the spectra are determined by sub-band filtering and fast Fourier transformation. Results. The resulting electric field spectra fall off to higher frequencies. An average electric field spectrum is fitted with an exponential Eν = K · exp (ν/MHz/β )a ndβ = −0.017 ± 0.004, or alternatively, with a power law � ν = K · ν α and a spectral index of α = −1 ± 0.2. The spectral slope obtained is not consistent within uncertainties and it is slightly steeper than the slope obtained from Monte Carlo simulations based on air showers simulated with CORSIKA (Cosmic Ray Simulations for KASCADE). For the analyzed sample of LOPES events, we do not find any significant dependence of the spectral slope on the electric field amplitude, the azimuth angle, the zenith angle, the curvature radius, nor on the average distance of the antennae from the shower core position. But one of the strongest events was measured during thunderstorm activity in the vicinity of LOPES and shows the longest pulse length measured of 110 ns and a spectral slope of α = −3.6. Conclusions. We show with two different methods that frequency spectra from air shower radio emission can be reconstructed on event-by-event basis, with only two dozen dipole antennae simultaneously over a broad range of frequencies. According to the obtained spectral slopes, the maximum power is emitted below 40 MHz. Furthermore, the decrease in power to higher frequencies indicates a loss in coherence determined by the shower disc thickness. We conclude that a broader bandwidth, larger collecting area, and longer baselines, as will be provided by LOFAR, are necessary to further investigate the relation of the coherence, pulse length, and spectral slope of cosmic ray air showers.

Radio detection of cosmic ray air showers with LOPES

Cosmic ray air showers are high energetic particles coming from the Universe toward the Earth every second. It is well known that they generate electromagnetic waves in the Earth atmosphere detectable on the ground. LOPES is an interferometric array of simple dipole radio * Paper presented at the National Conference on Physics, September 23–25, 2010, Iasi, Romania. 2 Radio detection of cosmic ray air showers with LOPES 309 antennas designed to measure radio signals initiated by cosmic air showers. It is working in coincidence with the particle detector array KASCADE-Grande at Karlsruhe Institute of Technology (KIT), campus North, from where receives the well-reconstructed shower observables. Determination of the emission mechanism is an important issue for LOPES, and here polarization measurements can play an important role. For first hints towards the verification of the radio emission mechanism, a comparison between measured data and an analytical approach is elaborated.

Radio Detection of Cosmic Ray Air Showers With Lopes

Cosmic ray air showers are high energetic particles coming from the Universe toward the Earth every second. It is well known that they generate electromagnetic waves in the Earth atmosphere detectable on the ground. LOPES is an interferometric array of simple dipole radio * Paper presented at the National Conference on Physics, September 23–25, 2010, Iasi, Romania. 2 Radio detection of cosmic ray air showers with LOPES 309 antennas designed to measure radio signals initiated by cosmic air showers. It is working in coincidence with the particle detector array KASCADE-Grande at Karlsruhe Institute of Technology (KIT), campus North, from where receives the well-reconstructed shower observables. Determination of the emission mechanism is an important issue for LOPES, and here polarization measurements can play an important role. For first hints towards the verification of the radio emission mechanism, a comparison between measured data and an analytical approach is elaborated.

Detecting radio pulses from air showers

Cosmic rays are energetic particles from outside the earth’s atmosphere. When a high energy cosmic ray hits the atmosphere it triggers a cascade of secondary particles produced in nuclear interactions, an air shower. Up to now the established methods of measuring air showers are detection of the particles that reach the ground level or optical observation of the Cherenkov or fluorescent light.

Air shower radio detection with LOPES

LOPES is an array of 30 radio antenna co-located with the KASCADE-Grande extensive air shower detector in Karlsruhe, Germany. It is designed as a digital radio interferometer for the detection of radio emission from extensive air showers. LOPES features high bandwidth and fast data processing. A unique asset is the concurrent operation with KASCADE-Grande. We report about the progress in understanding the radio signals measured by LOPES. In addition, the status and further perspectives of LOPES and the large scale application of this novel detection technique are sketched.