Expected performance of air-shower measurements with the radio-interferometric technique

Abstract

Interferometric measurements with arrays of radio antennas are a powerful and widely used technique in astronomy. Recently, this technique has been revisited for the reconstruction of extensive air showers []. This “radio-interferometric technique” exploits the coherence in the radio emission emitted by billions of secondary shower particles to reconstruct the shower parameters, in particular the shower axis and depth of the shower maximum X max. The accuracy previously demonstrated on simulations with an idealized detector is very promising. The prospect of an accurate X max measurement for inclined air showers combined with measurements of the electromagnetic energy (also with radio antennas) and the muonic shower content (via ground particle detectors) is very intriguing as it would provide a high sensitivity to the mass of cosmic rays, key information to study their origin. In this article we evaluate the potential of interferometric X max measurements using (simulated) inclined air showers with sparse antenna arrays under realistic conditions. To determine prerequisites for the application of the radio-interferometric technique with various antenna arrays, the influence of inaccuracies in the time synchronisation between antennas and its inter-dependency with the antenna density is investigated in detail. We find a strong correlation between the antenna multiplicity (per event) and the maximum acceptable time jitter, i.e., inaccuracy in the time synchronisation. For data recorded with a time synchronisation accurate to within 1 ns in the commonly used frequency band of 30 MHz to 80 MHz, an antenna multiplicity of >50 is needed to achieve an X max resolution of g cm−2. For data recorded with 2 ns accuracy, already ≳ 200 antennas are needed to achieve this X max resolution. Furthermore, we find no advantage reconstructing X max from data simulated at higher observation frequencies, i.e., up to several hundred MHz. Finally, we provide a generalisation of our results from very inclined air showers to vertical geometries.