Radio emission from extensive air showers as a method for cosmic-ray detection
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EMENTARY PARTICLES AND FIELDS Experiment
Radio Emission from Extensive Air Showers as a Method for Cosmic-Ray Detection N. N. Kalmykov, A. A. Konstantinov* , and R. Engel1) Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, 119991 Russia Received May 27, 2009; in final form, December 18, 2009
Abstract—At the present time, radio emission from extensive air showers (EASs) is being considered as a new promising method for detecting cosmic rays of energy in the region E0 > 5 × 1016 eV. Radio emission from an EAS whose development is simulated by the Monte Carlo method is calculated here. The field of radio emission from an EAS is calculated on the basis of two representations of a shower: that as a set of individual particles and that as a continuous set of currents. The sensitivity of radio emission to EAS parameters in the frequency range 10–100 MHz is investigated. The results can be used to analyze experiments that being presently performed (CODALEMA and LOPES) and those that are being planned for the future. DOI: 10.1134/S1063778810070136
1. INTRODUCTION An extremely low flux of cosmic rays is the main obstacle to detecting them. In the region of energies above 1015 eV, direct measurements are impossible, so that one has to resort to detecting secondary particles forming an extensive air shower (EAS) in the atmosphere. The detection of EASs is performed at the present time by measuring the flux of charged particles (primarily the electron–photon and muon components of the shower) and by observing optical radiations (Cherenkov light and fluorescence) generated by EASs at all stages of their development in the atmosphere. The idea of detecting cosmic rays by coherent radio emission from EASs was proposed by Askar’yan as far back as 1961 [1]. However, relevant experiments performed in the 1960s and 1970s did not lead to definitive results [2, 3]. Interest in radio emission from EASs have been quickened in recent years. Two arrays aimed at studying it, CODALEMA in France in the frequency range 30–65 MHz [4] and LOPES in Germany in the frequency range 40–80 MHz [5], are operating at the present time. According to data from the two experiments, the lower threshold for the detection of radio signals from EASs in the frequency range 10– 100 MHz is about 5 × 1016 eV. The detection of cosmic rays by radio emission has the following advantages in relation to other detection methods: radio antennas are relatively cheap 1) *
Karlsruhe Institute of Technology, Karlsruhe, Germany. E-mail: [email protected]
and simple in operation; moreover, the radio detection of EASs is independent of the time of day and of weather conditions, which are of importance for optical radiations (clear moonless nights constitute only 10% of the astronomic time). Also, fluctuations of the refractive index of the Earth’s atmosphere are known to be one of the sources of uncertainties in detecting Vavilov–Cherenkov optical radiation from EASs, but, in the case of radio emission in the frequency region below 100 MHz, these fluctuations ca
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