Calibration of the absolute amplitude scale of the Tunka Radio Extension (ICRC 2015)

TL;DR

This paper details the calibration process of the Tunka-Rex radio array, establishing a consistent absolute amplitude scale across multiple experiments, and compares measurements with simulations to validate the calibration accuracy.

Contribution

It introduces a calibration method for Tunka-Rex's antennas using a commercial reference source, aligning its scale with LOPES and LOFAR, and resolves previous measurement discrepancies.

Findings

Calibration achieved with 18% scale uncertainty.

Radio measurements agree with CoREAS simulations.

Established a consistent absolute amplitude scale across experiments.

Abstract

The Tunka Radio Extension (Tunka-Rex) is an array of 44 radio antenna stations, distributed over 3 km$^{2}$, constituting a radio detector for air showers with an energy threshold around 10$^{17}$ eV. It is an extension to Tunka-133, an air-Cherenkov detector in Siberia, which is used as an external trigger for Tunka-Rex and provides a reliable reconstruction of energy and shower maximum. Each antenna station consists of two perpendicularly aligned active antennas, called SALLAs. An antenna calibration of the SALLA with a commercial reference source enables us to reconstruct the detected radio signal on an absolute scale. Since the same reference source was used for the calibration of LOPES and, in a calibration campaign in 2014, also for LOFAR, these three experiments now have a consistent calibration and, therefore, absolute scale. This was a key ingredient to resolve a longer standing contradiction between measurements of two calibrated experiments. We will present how the calibration was performed and compare radio measurements of air showers from Tunka-Rex to model calculations with the radio simulation code CoREAS, confirming it within the scale uncertainty of the calibration of 18%.