Abstract
Since 2003, significant efforts have been devoted to the understanding of the radio emission of extensive air shower in the range [20-200] MHz. Despite some studies led until the early nineties, the [1-10] MHz band has remained unused for 20 years. However, it has been measured by some pioneering experiments that extensive air shower emit a strong electric field in this band and that there is evidence of a large increase in the amplitude of the radio pulse at lower frequencies. The EXTASIS experiment, located within the Nançay Radioastronomy Observatory and supported by the CODALEMA experiment, aims to reinvestigate the [1-10] MHz band, and especially to study the so-called “Sudden Death” contribution, the expected electric field emitted by shower front when hitting the ground level. Currently, EXTASIS has confirmed some results obtained by the pioneering experiments, and tends to bring explanations to the other ones, for instance the role of the underlying atmospheric electric field. Moreover, CODALEMA has demonstrated that in the most commonly used frequency band ([20-80] MHz) the electric field profile of EAS can be well sampled, and contains all the information needed for the reconstruction of EAS: an automatic comparison between the SELFAS3 simulations and data has been developed, allowing us to reconstruct in an almost real time the primary cosmic ray characteristics.
Highlights
It is a well known fact that a coherent radio emission is emitted during the development of air shower through the transverse charged current variation induced by the geomagnetic field, and the charge excess mechanism [1,2,3]
The resulting electric field can be detected by large bandwidth antennas and fast acquisition systems
The characteristics of the primary cosmic rays can be estimated by comparing the electric field detected at ground level to the simulated ones, as described in the following
Summary
It is a well known fact that a coherent radio emission is emitted during the development of air shower through the transverse charged current variation induced by the geomagnetic field, and the charge excess mechanism [1,2,3]. CODALEMA is hosted since 2002 by the Nançay Radioastronomy Observatory It is one of the pioneering experiments that have participated in the rebirth of radio detection of cosmic rays. The experiment has seen the development of a large collection of detectors, intended to study the properties of the radio emission associated with cosmic ray induced air showers in the energy range from 1016 to 1018 eV. A so-called “Compact Array” of 10 cross-polarized antennas, arranged in a star shape of 150 m extension and whose signal acquisition (in the MF band) is triggered by the particle detector. CODALEMA is today the supporting experiment of EXTASIS, an array of 7 low-frequency antennas triggered by the particle detector.
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