Geomagnetic effects observed by the CODALEMA experiment

The CODALEMA experiment is measuring transient radio emissions associated to extended air showers produced by high energy cosmic rays. The experimental setup installed at the Nançay Radio Observatory in France has recently undergone hardware upgrades and an extension of the surfaces covered by both the antenna and the scintillator detector arrays. The experimental data allow to investigate the main features of these radio signals and the underlying electric field production mechanisms. Some of the latest experimental results of CODALEMA are presented. They have been analyzed assuming a linear dependence of the electric field with respect to v ∧ B . Within the CODALEMA observation conditions at Nançay, the detection efficiency, the arrival direction distribution and the polarity of the radio signals can be interpreted in terms of a geomagnetic effect. A R&D effort is currently underway to develop the hardware elements for the deployment of a large detector array based on active antennas. The main features of the first prototype of the CODALEMA autonomous station are briefly described.