A novel method for the absolute energy calibration of large-scale cosmic-ray detectors using radio emission of extensive air showers

Ultra-high energy cosmic rays impinging onto the atmosphere induce huge cascades of secondary particles. The measurement of the energy radiated by these air showers in form of radio waves enables an accurate measurement of the cosmic-ray energy. Compared to the well-established fluorescence technique, the radio measurements are less dependent on atmospheric conditions and thus potentially reduce the systematic uncertainty in the cosmic-ray energy measurement significantly. Two attractive aspects are that the atmosphere is transparent to MHz radio waves and the radio emission can be calculated from first-principles using classical electrodynamics. This method will be discussed for the Engineering Radio Array (AERA) of the Pierre Auger Cosmic-Ray Observatory. AERA detects radio emission from extensive air showers with energies beyond ${10}^{17}$eV in the 30 - 80 MHz frequency band and consists of more than 150 autonomous radio stations covering an area of about 17$$km${}^2$. It is located at the same site as the Auger low-energy detector extensions enabling combinations with various other measurement techniques.