Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory

TL;DR

This paper presents a method for estimating cosmic-ray energies using radio emissions detected by the AERA array, calibrated against surface detector data, demonstrating a quadratic scaling and a 22% energy resolution.

Contribution

It introduces a calibrated radio-based energy estimator for cosmic rays that scales quadratically with energy and achieves high resolution, enhancing cosmic-ray detection methods.

Findings

Radio energy scales quadratically with cosmic-ray energy

Achieved 22% energy resolution for radio reconstruction

Measured 15.8 MeV of radiation energy for 1 EeV air showers

Abstract

The Auger Engineering Radio Array (AERA) is part of the Pierre Auger Observatory and is used to detect the radio emission of cosmic-ray air showers. These observations are compared to the data of the surface detector stations of the Observatory, which provide well-calibrated information on the cosmic-ray energies and arrival directions. The response of the radio stations in the 30 to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of the incoming electric field. For the latter, the energy deposit per area is determined from the radio pulses at each observer position and is interpolated using a two-dimensional function that takes into account signal asymmetries due to interference between the geomagnetic and charge-excess emission components. The spatial integral over the signal distribution gives a direct measurement of the energy transferred from the primary cosmic ray into radio emission in the AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air shower arriving perpendicularly to the geomagnetic field. This radiation energy -- corrected for geometrical effects -- is used as a cosmic-ray energy estimator. Performing an absolute energy calibration against the surface-detector information, we observe that this radio-energy estimator scales quadratically with the cosmic-ray energy as expected for coherent emission. We find an energy resolution of the radio reconstruction of 22% for the data set and 17% for a high-quality subset containing only events with at least five radio stations with signal.