A method for high precision reconstruction of air shower Xmax using two-dimensional radio intensity profiles

摘要

The mass composition of cosmic rays contains important clues about theirorigin. Accurate measurements are needed to resolve long-standing issues suchas the transition from Galactic to extragalactic origin, and the nature of thecutoff observed at the highest energies. Composition can be studied bymeasuring the atmospheric depth of the shower maximum Xmax of air showersgenerated by high-energy cosmic rays hitting the Earth's atmosphere. We presenta new method to reconstruct Xmax based on radio measurements. The radioemission mechanism of air showers is a complex process that creates anasymmetric intensity pattern on the ground. The shape of this pattern stronglydepends on the longitudinal development of the shower. We reconstruct Xmax byfitting two-dimensional intensity profiles, simulated with CoREAS, to data fromthe LOFAR radio telescope. In the dense LOFAR core, air showers are detected byhundreds of antennas simultaneously. The simulations fit the data very well,indicating that the radiation mechanism is now well-understood. The typicaluncertainty on the reconstruction of Xmax for LOFAR showers is 17 g/cm^2.