Improved absolute calibration of LOPES measurements and its impact on the comparison with REAS 3.11 and CoREAS simulations

Abstract LOPESwas a digital antenna array detecting the radio emission of cosmic-ray air showers. The calibration of the absolute amplitude scale of the measurements was done using an external, commercial reference source, which emits a frequency combwith defined amplitudes. Recently, we obtained improved reference values by the manufacturer of the reference source, which significantly changed the absolute calibration of LOPES. We reanalyzed previously published LOPESmeasurements, studying the impact of the changed calibration. The main effect is an overall decrease of the LOPESamplitude scale by a factor of 2.6 ± 0.2, affecting all previously published values for measurements of the electric-field strength. This results in a major change in the conclusion of the paper ‘Comparing LOPESmeasurements of air-showerradio emission with REAS 3.11 and CoREAS simulations’ published by Apel et al. (2013) : With the revised calibration, LOPESmeasurements now are compatible with CoREAS simulations, but in tension with REAS 3.11 simulations. Since CoREAS is the latest version of the simulation code incorporating the current state of knowledge on the radio emission of air showers, this new result indicates that the absolute amplitude prediction of current simulations now is in agreement with experimental data.