AERA is a new antenna system to measure short radio pulses emitted by cosmic ray air showers of the highest energies. It consists of an array of dozens of antennas sensitive in the frequency range of 30 to 80 MHz with signal processing and electronics developed specifically for this purpose.
AERA antennas are active 24 hours a day, like the surface detectors of the Pierre Auger Observatory. Radio detection of cosmic rays has been applied first over 50 years ago, but only with the digital signal processing available today it could be implemented on large scales yielding detailed and high-quality measurements.
At the time of writing, 124 AERA radio stations covering an area of 6 km2 are in operation. The 124 stations have been deployed in two steps. AERA-24 was deployed in 2010 and consisted of 24 radio stations equipped with LPDA (logarithmic-periodic dipole) antennas on a grid with 150 m antenna separation. Then in May 2013, 100 stations of a different design using so-called "butterfly antennas" were added. The 100 new stations in AERA-124 are spaced 250 m or 375 m apart from each other. Additional prototype stations with the ability to measure the electric field vector in 3D and at lower frequencies were also installed. In spring 2015, 25 more antenna stations will be deployed on a grid with up to 750 m antenna separation, increasing the instrumented area significantly and allowing improved studies of horizontal air showers.
AERA is regularly detecting cosmic rays in coincidence with the particle and fluorescence detectors of the Pierre Auger Observatory. Initial analyses have already led to significant first results, in particular confirming the theoretical predictions of the emission mechanism. Monte Carlo simulations are in good agreement with the data and analyses to extract detailed characteristics of the measured air showers are ongoing.