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

Abstract

a b s t r a c tThe 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 R 0 , describing the slope of the lateral profiles range between 100 and 200 m. No evidence for a direct correlation of R 0 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.

Comparing LOPES measurements of air-shower radio emission with REAS 3.11 and CoREAS simulations

“…Thus, we have decided to use an exponential LDF with an amplitude and a slope parameter, as already in Refs. [24,25] -in particular since a power law as alternative 2-parameter LDF has been shown to be inappropriate for LOPES events [24].…”

“…[24]: First, we use the amplitude at an axis distance of 100 m as fit parameter instead of the amplitude at the shower core, since 100 m is close to the mean axis distance of about 120 m and close to the distance where least fluctuations due to the primary particle type are expected for LOPES (70 − 90 m) [49]. This reduces the uncertainty of the amplitude fit parameter while still describing the same physics.…”

“…Although a scale uncertainty is not important when comparing several LOPES events with each other (as in Ref. [24]), it is crucial when comparing LOPES events with other experiments or simulations. In particular, the scale uncertainty limits the testing power whether a theoretical model can predict the absolute amplitude correctly.…”

“…The lateral distribution of the radio signal is the variation of the radio amplitude ǫ with the distance to air shower axis d. It has already been studied with LOPES [24,25] and other experiments (e.g., CODALEMA [12]), and already it was compared to simulations [26], however, only for single events or with a limited statistics. These limited studies had been sufficient to show that earlier models, not yet including the refractive index of the air, could not fully reproduce the measurements.…”

Results of a self-triggered prototype system for radio-detection of extensive air showers at the Pierre Auger Observatory

“…Therefore, the direct estimation of both E EW 0 and d 0 for each event is not possible. Nevertheless, it is still possible to obtain an estimation of the electric field value E EW 0 , assuming the parameter d 0 to be 150 m as suggested by the CODALEMA [29] and LOPES [30] experiments. We also have to rescale E EW 0 to a normalized value depending on the incoming arrival direction and the geomagnetic field n × B.…”