Geomagnetic origin of the radio emission from cosmic ray induced air showers observed by CODALEMA

Abstract The new setup of the CODALEMA experiment installed at the Radio Observatory in Nancay, France, is described. It includes broadband active dipole antennasand an extended and upgraded particle detectorarray. The latter gives access to the air showerenergy, allowing us to compute the efficiency of the radio array as a function of energy. We also observe a large asymmetry in counting rates between showerscoming from the North and the South in spite of the symmetry of the detector. The observed asymmetry can be interpreted as a signature of the geomagnetic origin of the air showerradio emission. A simple linear dependence of the electric field with respect to v ∧ B is used which reproduces the angular dependencies of the number of radio events and their electric polarity.