First Data of the 3000km2 Radio Detector at the Pierre Auger Observatory

In this contribution, we present the status and first data from the Radio Detector (RD) at the Pierre Auger Observatory, consisting of 1660 radio antennas deployed across the 3000 km2 surface detector array. These antennas measure the radio emission from extensive air showers in the 30 − 80 MHz band, enabling electromagnetic energy measurements for air showers with zenith angles above 65 ◦. Combined with the muonic measurements from the water-Cherenkov detectors (WCDs), this allows mass composition studies at the highest energies. The large-scale deployment of the RD began in November 2023 and was completed in November 2024. A full end-to-end calibration shows consistency between Galactic and in-lab calibration to better than 5% and includes continuous monitoring for hardware failures, ensuring, for example, antenna alignment within 5 ◦. We present the first data, demonstrating a strong correlation between the electromagnetic energy measured by the RD and the total shower energy measured by the WCD, confirming that the detector chain—including triggering, data readout, absolute calibration, and reconstruction is well understood. We highlight a particularly impressive 32 EeV shower at a zenith angle of 85 ◦, producing a 50 km-long radio footprint, showcasing the unique capabilities of this detector.