Revised absolute amplitude calibration of the LOPES experiment

Abstract One of the main aims of the LOPESexperiment was the evaluation of the absolute amplitudeof the radio signal of air showers. This is of special interest since the radio technique offers the pos- sibilityfor an independent and highly precise determination of the energy scale of cosmic rays onthe basis of signal predictions from Monte Carlo simulations. For the calibration of the amplitudemeasured by LOPESwe used an external source. Previous comparisons of LOPESmeasurementsand simulations of the radio signal amplitude predicted by CoREAS revealed a discrepancy of theorder of a factor of two. A re-measurement of the reference calibration source, now performed forthe free field, was recently performed by the manufacturer. The updated calibration values leadto a lowering of the reconstructed electric field measured by LOPESby a factor of 2:6 0:2 andtherefore to a significantly better agreement with CoREAS simulations. We discuss the updatedcalibration and its impact on the LOPESanalysis results.2