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Abstract
We reconstructed the energy and the position of the shower maximum of air showers with energies E ≳ 100 PeV applying a method using radio measurements performed with Tunka-Rex. An event-to-event comparison to air-Cherenkov measurements of the same air showers with the Tunka-133 photomultiplier array confirms that the radio reconstruction works reliably. The Tunka-Rex reconstruction methods and absolute scales have been tuned on CoREAS simulations and yield energy and Xmax values consistent with the Tunka-133 measurements. The results of two independent measurement seasons agree within statistical uncertainties, which gives additional confidence in the radio reconstruction. The energy precision of Tunka-Rex is comparable to the Tunka-133 precision of 15%, and exhibits a 20% uncertainty on the absolute scale dominated by the amplitude calibration of the antennas. For Xmax, this is the first direct experimental correlation of radio measurements with a different, established method. At the moment, the Xmax resolution of Tunka-Rex is approximately 40 g/cm2. This resolution can probably be improved by deploying additional antennas and by further development of the reconstruction methods, since the present analysis does not yet reveal any principle limitations.
Highlights
The main origin of the radio emission is the geomagnetic deflection of relativistic electrons and positrons in the shower, which induces a time-variable current [9]
The background remaining after filtering still on average increases the measured pulse height Emeas compared to the true pulse height Etrue, as already seen at the LOPES experiment [27] and assumed for early experiments [28]. We studied this effect by adding measured background to about 300 CoREAS simulations, and found that the parametrization given in reference [27] has to be slightly modified introducing a normalization factor k = 4.1 adapted for Tunka-Rex
There is a clear correlation between the energy reconstructed from the radio amplitude measured by Tunka-Rex and the energy reconstructed from the air-Cherenkov light measured by Tunka-133
Summary
The main origin of the radio emission is the geomagnetic deflection of relativistic electrons and positrons in the shower, which induces a time-variable current [9]. Tunka-133 is fully efficient for all zenith angles θ ≤ 50◦ at energies above 1016.2 eV [18], which covers the full energy range of Tunka-Rex. For Tunka-133 measurements, the energy of the primary particle Epr is reconstructed from the flux of the Cherenkov light at 200 m distance to the shower axis, and Xmax is reconstructed from the steepness of the amplitude-distance function. In particular the precision of Tunka-Rex is estimated by a comparison of the energy and Xmax reconstructions to Tunka-133. First results on energy and Xmax reconstruction have already been presented in reference [25] using the first season of Tunka-Rex measurements from October 2012 to April 2013 (effectively 280 hours of measurements). In the experimental data we observe a direct correlation between the Tunka-Rex and Tunka-133 reconstructions, which is used to estimate precision and accuracy of Tunka-Rex for energy and Xmax
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