Event reconstruction with the Radio detector of the Pierre Auger Observatory

The surface detector of the Pierre Auger Observatory has recently been upgraded with the addition
of radio antennas, forming the radio detector (RD). This contribution outlines the standard methods
for reconstructing extensive air showers using the RD, along with recent developments.
The reconstruction pipeline is based on a robust understanding of the detector itself. The entire
instrument, including the antenna pattern and analog chain, has been meticulously characterized
within the Offline software framework, based on measurements in the laboratory as well as in the
field. To ensure data integrity, stations identified as unreliable through monitoring are excluded
before event reconstruction. Absolute calibration is achieved at the 5% level by analyzing the
diffuse galactic radio emission. Next, the electric field that induced voltages in the antenna is
calculated by “unfolding” the antenna response pattern. Key observables, such as the energy
fluence (the energy deposited in the ground per unit area) and the arrival time of the pulse,
are then determined. With these quantities, shower parameters can be reconstructed with very
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good accuracy in two 𝜒2-minimization fits: one to determine the shower’s arrival direction via a
spherical wavefront fit (predicted within 0.2°), and the other to estimate the distance to the shower
maximum and the electromagnetic cascade energy (predicted within 5%) using a lateral density
function.