Long-term calibration and validation of stability of the Auger Engineering Radio Array using the diffuse Galactic radio emission

Abstract

The Auger Engineering Radio Array (AERA) measures radio emission from high-energy extensive air showers. Consisting of 153 autonomous radio-detector stations spread over $17$\,km$^2$, it detects radio waves in the frequency range of $30$ to $80$\,MHz. Accurate characterization of the detector response is crucial for proper interpretation of the collected data. Previously, this was achieved through laboratory measurements of the analog chain and simulations and measurements of the antenna's directional response. In this paper, we perform an absolute calibration using the continuously monitored sidereal modulation of the diffuse Galactic radio emission. Calibration is done by comparing the average frequency spectra recorded by the stations with predictions from seven different models of the full radio sky, accounting for the system response, which includes the antenna, filters, and amplifiers. The analysis of the calibration constants over a period of seven years shows no relevant and no significant ageing effect in the AERA antennas. This result confirms the long-term stability of the detector stations and demonstrates the possibility for a radio detector to effectively monitor ageing effects of other detectors operating over extended periods.

Figures (9)

• Figure 1: Dynamic average frequency spectrum as a function of LST for the north-south channel of one of the antennas during February 2019. The left panel presents the results before removal of narrowband RFI (horizontal lines), while the right panel shows that the Galactic signal variation becomes evident after RFI removal.
• Figure 2: Average spectral density for one of the antennas during January 2019 as a function of LST for the north-south channel, before the removal of broadband RFI (left) and after the removal (right).
• Figure 3: The left (right) panel shows the expected power $P_{\rm{sky}}$ to be received from the sky considering the LFmap model and the simulated VEL of butterfly antennas, in frequency bins of 1 MHz and LST bins of 1 hour, as a function of LST and frequency for the north–south (east–west) channel.
• Figure 4: Averaged power over frequencies for each radio sky temperature model propagated through the antenna pattern as a function of time. Panels on the left and right represent the north-south and east-west polarizations, respectively. Panels above (below) correspond to butterfly antennas (LPDAs). The solid black line represents the average model, and the shaded areas indicate two standard deviations of the average power distribution calculated for each antenna after correction with the calibration constants and average noise of all models.
• Figure 5: Left panel: measured power versus the expected power, and the resulting linear fits obtained for each frequency bin. Each fit is based on 24 points corresponding to hourly LST bins. The results correspond to the north-south channel of one of the antennas, using periodic all-triggered traces collected during January 2019. Right panel: calibration constants $C_0^2$ (top panel) and total noise $N_{\rm{tot}}$ (bottom panel) obtained from the fit.