A Rotationally Symmetric Lateral Distribution Function for Radio Emission from Inclined Air Showers

Radio detection of inclined air showers is currently receiving great attention. To exploit the potential, a suitable event reconstruction needs to be developed. The first step in this direction is the development of a model for the lateral distribution of the radio signals, which in the case of inclined air showers exhibits asymmetries due to "early-late" effects in addition to the usual asymmetries from the superposition of charge-excess and geomagnetic emission. We present a model which corrects for all asymmetries and successfully describes the lateral distribution of the energy fluence with a rotationally symmetric function. This gives access to the radiation energy as a measure of the energy of the cosmic-ray primary, and is also sensitive to the depth of the shower maximum.Comment: To be published in the proceedings of the ARENA2018 conference; revised version with important fix of former equation (2

Symmetrizing the signal distribution of radioemission from inclined air showers

Radio detection of inclined air showers currently receives special attention. It can be performed with very sparse antenna arrays and yields a pure measurement of the electromagnetic air-shower component, thus delivering information that is highly complementary to the measurement of the muonic component using particle detectors. However, radio-based reconstruction of inclined air showers is challenging in light of asymmetries induced in the radio-signal distribution by early-late effects as well as the superposition of geomagnetic and charge-excess radiation. We present a model for the signal distribution of radio emission from inclined air showers which allows explicit compensation of these asymmetries. In a first step, geometrical early-late asymmetries are removed. Secondly, a universal parameterization of the charge-excess fraction as a function of the air-shower geometry, the atmospheric density profile and the lateral distance from the shower axis is used to compensate for the charge-excess contribution to the signal. The resulting signal distribution of the pure geomagnetic emission is then fit with a rotationally symmetric lateral distribution function, the area integration of which yields the radiation energy as an estimator for the cosmic-ray energy. We present the details and performance of our model, which lays the foundation for robust and precise reconstruction of inclined air showers from radio measurements.Comment: Proceedings of the 36th ICRC, Madison, WI, USA, PoS(ICRC2019)294; v2 updated to final published version with slight changes of fit values in section 6 and Fig. 8 due to correction of a mixu

Reconstructing the cosmic-ray energy from the radio signal measured in one single station

Short radio pulses can be measured from showers of both high-energy cosmic rays and neutrinos. While commonly several antenna stations are needed to reconstruct the energy of an air shower, we describe a novel method that relies on the radio signal measured in one antenna station only. Exploiting a broad frequency bandwidth of $80-300$ MHz, we obtain a statistical energy resolution of better than 15\% on a realistic Monte Carlo set. This method is both a step towards energy reconstruction from the radio signal of neutrino induced showers, as well as a promising tool for cosmic-ray radio arrays. Especially for hybrid arrays where the air shower geometry is provided by an independent detector, this method provides a precise handle on the energy of the shower even with a sparse array

Reconstructing inclined extensive air showers from radio measurements

We present a reconstruction algorithm for extensive air showers with zenith angles between 65$^\circ$ and 85$^\circ$ measured with radio antennas in the 30-80 MHz band. Our algorithm is based on a signal model derived from CoREAS simulations which explicitly takes into account the asymmetries introduced by the superposition of charge-excess and geomagnetic radiation as well as by early-late effects. We exploit correlations among fit parameters to reduce the dimensionality and thus ensure stability of the fit procedure. Our approach reaches a reconstruction efficiency near 100% with an intrinsic resolution for the reconstruction of the electromagnetic energy of well below 5\%. It can be employed in upcoming large-scale radio detection arrays using the 30-80 MHz band, in particular the AugerPrime Radio detector of the Pierre Auger Observatory, and can likely be adapted to experiments such as GRAND operating at higher frequencies.Comment: Proceedings of the ICRC2021 conferenc

Reconstructing inclined extensive air showers from radio measurements

We present a reconstruction algorithm for extensive air showers with zenith angles between 65$^\circ$ and 85$^\circ$ measured with radio antennas in the 30-80 MHz band. Our algorithm is based on a signal model derived from CoREAS simulations which explicitly takes into account the asymmetries introduced by the superposition of charge-excess and geomagnetic radiation as well as by early-late effects. We exploit correlations among fit parameters to reduce the dimensionality and thus ensure stability of the fit procedure. Our approach reaches a reconstruction efficiency near 100% with an intrinsic resolution for the reconstruction of the electromagnetic energy of well below 5\%. It can be employed in upcoming large-scale radio detection arrays using the 30-80 MHz band, in particular the AugerPrime Radio detector of the Pierre Auger Observatory, and can likely be adapted to experiments such as GRAND operating at higher frequencies.Comment: Proceedings of the ICRC2021 conferenc

Signal model for the reconstruction of inclined air showers with sparse radio arrays

We present a signal- and reconstruction model for the radio emission of extensive air showers with zenith angles between 65∘ and 85∘ in the 30 - 80 MHz band. The model is derived from CoREAS simulations and explicitly takes into account the asymmetries introduced by the superposition of charge-excess and geomagnetic radiation as well as by early-late effects. We exploit correlations among fit parameters to reduce the dimensionality, thereby ensuring stability of the fit procedure. Our approach reaches a reconstruction efficiency near 100% with an intrinsic resolution for the reconstruction of the electromagnetic energy below 5% using a 1.5km-sparse antenna array. It can be employed in upcoming large-scale radio detection arrays using the 30-80 MHz band, in particular the Auger Radio detector of the upgraded Pierre Auger Observatory, and can likely be adapted to experiments such as GRAND operating at higher frequencies

Signal model and event reconstruction for the radio detection of inclined air showers

The detection of inclined air showers (zenith angles θ ≳ 65°) with kilometer-spaced radio-antenna arrays allows measuring cosmic rays at ultra-high energies (E ≲ 10$^{20}$ eV). Radio and particle detector arrays provide independent measurements of the electromagnetic and muonic shower components of inclined air showers, respectively. Combined, these measurements have a large sensitivity to discriminate between air showers initiated by lighter and heavier cosmic rays. We have developed a precise model of the two-dimensional, highly complex and asymmetric lateral radio-signal distributions of inclined air shower at ground — the "radio-emission footprints". Our model explicitly describes the dominant geomagnetic emission with a rotationally symmetric lateral distribution function, on top of which additional effects disturb the symmetry. The asymmetries are associated with the interference between the geomagnetic and sub-dominant charge-excess emission as well as with geometrical projection effects, so-called "early-late" effects. Our fully analytic model describes the entire footprint with only two observables: the geometrical distance between the shower impact point at the ground and the shower maximum d$_{max}$, and the geomagnetic radiation energy E$_{geo}$. We demonstrate that with this model, the electromagnetic shower energy can be reconstructed by kilometer-spaced antenna arrays with an intrinsic resolution of 5% and a negligible bias

Refractive displacement of the radio-emission footprint of inclined air showers simulated with CoREAS

The footprint of radio emission from extensive air showers is known to exhibit asymmetries due to the superposition of geomagnetic and charge-excess radiation. For inclined air showers a geometric early-late effect disturbs the signal distribution further. Correcting CoREAS simulations for these asymmetries reveals an additional disturbance in the signal distribution of highly inclined showers in atmospheres with a realistic refractive index profile. This additional apparent asymmetry in fact arises from a systematic displacement of the radio-emission footprint with respect to the Monte-Carlo shower impact point on the ground. We find a displacement of ∼1500 m in the ground plane for showers with a zenith angle of 85°, illustrating that the effect is relevant in practical applications. A model describing this displacement by refraction in the atmosphere based on Snell’s law yields good agreement with our observations from CoREAS simulations. We thus conclude that the displacement is caused by refraction in the atmosphere