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Register a new userTheory and simulations of air shower radio emission
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T. Huege
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A precise understanding of the radio emission from extensive air showers is of fundamental importance for the design of cosmic ray radio detectors as well as the analysis and interpretation of their data. In recent years, tremendous progress has been made in the understanding of the emission physics both in macroscopic and microscopic frameworks. A consistent picture has emerged: the emission stems mainly from time-varying transverse currents and a time-varying charge excess; in addition, Cherenkov-like compression of the emission due to the refractive index gradient in the atmosphere can lead to time-compression of the emitted pulses and thus high-frequency contributions in the signal. In this article, I discuss the evolution of the modelling in recent years, present the emission physics as it is understood today, and conclude with a description and comparison of the models currently being actively developed.
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Cosmic ray air showers emit radio pulses at MHz frequencies, which can be measured with radio antenna arrays - like LOPES at the Karlsruhe Institute of Technology in Germany. To improve the understanding of the radio emission, we test theoretical descriptions with measured data. The observables used for these tests are the absolute amplitude of the radio signal, and the shape of the radio lateral distribution. We compare lateral distributions of more than 500 LOPES events with two recent and public Monte Carlo simulation codes, REAS 3.11 and CoREAS (v 1.0). The absolute radio amplitudes predicted by REAS 3.11 are in good agreement with the LOPES measurements. The amplitudes predicted by CoREAS are lower by a factor of two, and marginally compatible with the LOPES measurements within the systematic scale uncertainties. In contrast to any previo
Accurate prediction of the radio emission from cosmic ray air showers relies on computationally demanding Monte Carlo simulations such as CoREAS. We aim to expedite this process via a semi-analytical synthesis model while maintaining high accuracy by using simulated radio pulses as templates. We present our key concept for template processing focusing on the development of the particle cascade and its empirical effect on the locally produced radio signal. In this context the universality of the radio emission from small sections of an air shower also becomes important where most previous studies focus on integral quantities observable at far distances.
Cosmic rays extensive air showers (EAS) are associated with transient radio emission, which could provide an efficient new detection method of high energy cosmic rays, combining a calorimetric measurement with a high duty cycle. The CODALEMA experiment, installed at the Radio Observatory in Nancay, France, is investigating this phenomenon in the 10^17 eV region. One challenging point is the understanding of the radio emission mechanism. A first observation indicating a linear relation between the electric field produced and the cross product of the shower axis with the geomagnetic field direction has been presented (B. Revenu, this conference). We will present here other strong evidences for this linear relationship, and some hints on its physical origin.
Relativistic, charged particles present in extensive air showers lead to a coherent emission of radio pulses which are measured to identify the shower initiating high-energy cosmic rays. Especially during thunderstorms, there are additional strong electric fields in the atmosphere, which can lead to further multiplication and acceleration of the charged particles and thus have influence on the form and strength of the radio emission. For a reliable energy reconstruction of the primary cosmic ray by means of the measured radio signal it is very important to understand how electric fields affect the radio emission. In addition, lightning strikes are a prominent source of broadband radio emissions that are visible over very long distances. This, on the one hand, causes difficulties in the detection of the much lower signal of the air shower. On the other hand the recorded signals can be used to study features of the lightning development. The detection of cosmic rays via the radio emission and the influence of strong electric fields on this detection technique is investigated with the LOPES experiment in Karlsruhe, Germany. The important question if a lightning is initiated by the high electron density given at the maximum of a high-energy cosmic-ray air shower is also investigated, but could not be answered by LOPES. But, these investigations exhibit the capabilities of EAS radio antenna arrays for lightning studies. We report about the studies of LOPES measured radio signals of air showers taken during thunderstorms and give a short outlook to new measurements dedicated to search for correlations of lightning and cosmic rays.
The influence of the geomagnetic field on the development of air showers is studied. The well known International Geomagnetic Reference Field was included in the AIRES air shower simulation program as an auxiliary tool to allow calculating very accurate estimations of the geomagnetic field given the geographic coordinates, altitude above sea level and date of a given event. Some test simulations made for representative cases indicate that some quantities like the lateral distribution of muons experiment significant modifications when the geomagnetic field is taken into account.
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