Interferometric Radio Measurements of Air Showers with LOPES: Final Results

LOPES was the radio extension of the KASCADE-Grande particle-detector array consisting of up to 30 antennas measuring the radio emission of cosmic-ray air showers between 40 and 80 MHz with an energy threshold of around 100 PeV. Even with the external trigger by the particle detectors, the separation of the air-shower signal from the radio background was difficult in the noisy environment of the Karlsruhe Institute of Technology. For the typical event this was only possible because of the digital, interferometric beamforming technique pioneered by LOPES for cosmic-ray detection. Using this technique LOPES made important discoveries with respect to the radio emission of air showers and their relation to the shower properties, such as its energy and its longitudinal development. By now, practically all results have been confirmed by subsequent antenna arrays, but regarding digital interferometry the LOPES results are still unique. Lately we completed an end-to-end pipeline for CoREAS simulations of the radio emission including measured background and all known detector responses as well as the interferometric analysis technique. As result we present an update on the reconstruction of the most important shower parameters: arrival direction, energy, and $X_\mathrm{max}$.