In 1965 it was discovered that cosmic ray air showers emit impulsive radio signals at frequencies below 100 MHz. After a period of intense research in the 1960s and 1970s, however, interest in the ...detection technique faded almost completely. With the availability of powerful digital signal processing techniques, new attempts at measuring cosmic ray air showers via their radio emission were started at the beginning of the new millennium. Starting with modest, small-scale digital prototype setups, the field has evolved, matured and grown very significantly in the past decade. Today’s second-generation digital radio detection experiments consist of up to hundreds of radio antennas or cover areas of up to 17 km2. We understand the physics of the radio emission in extensive air showers in detail and have developed analysis strategies to accurately derive from radio signals parameters which are related to the astrophysics of the primary cosmic ray particles, in particular their energy, arrival direction and estimators for their mass. In parallel to these successes, limitations inherent in the physics of the radio signals have also become increasingly clear. In this article, we review the progress of the past decade and the current state of the field, discuss the current paradigm of the radio emission physics and present the experimental evidence supporting it. Finally, we discuss the potential for future applications of the radio detection technique to advance the field of cosmic ray physics.
As part of the ongoing AugerPrime upgrade of the Pierre Auger Observatory, we are deploying short aperiodic loaded loop antennas measuring radio signals from extensive air showers in the 30 – 80 MHz ...band on each of the 1,660 surface detector stations. This new Radio Detector of the Observatory allows us to measure the energy in the electromagnetic cascade of inclined air showers with zenith angles larger than ∼ 65°. The water-Cherenkov detectors, in turn, perform a virtually pure measurement of the muon component of inclined air showers. The combination of both thus extends the mass-composition sensitivity of the upgraded Observatory to high zenith angles and therefore enlarges the sky coverage of mass-sensitive measurements at the highest energies while at the same time allowing us to cross-check the performance of the established detectors with an additional measurement technique. In this contribution, we outline the concept and design of the Radio Detector, report on its current status and initial results from the first deployed stations, and illustrate its expected performance with a detailed, end-to-end simulation study.
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.
Recently, the energy determination of extensive air showers using radio emission has been shown to be both precise and accurate. In particular, radio detection offers the opportunity for an ...independent measurement of the absolute energy scale of cosmic rays, since the radiation energy (the energy radiated in the form of radio signals) can be predicted using first-principle calculations involving no free parameters, and the measurement of radio waves is not subject to any significant absorption or scattering in the atmosphere. To quantify the uncertainty associated with such an approach, we collate the various contributions to the uncertainty, and we verify the consistency of radiation-energy calculations from microscopic simulation codes by comparing Monte Carlo simulations made with the two codes CoREAS and ZHAireS. We compare a large set of simulations with different primary energies and shower directions and observe differences in the radiation energy prediction for the 30–80 MHz band of 5.2%. This corresponds to an uncertainty of 2.6% for the determination of the absolute cosmic-ray energy scale. Our result has general validity and can be built upon directly by experimental efforts for the calibration of the cosmic-ray energy scale on the basis of radio emission measurements.
For more than 20 years, the community has heavily relied on CORSIKA for the simulation of extensive air showers, their Cherenkov light emission and their radio signals. While tremendously successful, ...the Fortran-based monolithic design of CORSIKA up to version 7 limits adaptation to new experimental needs, for example, in complex scenarios where showers transition from air into dense media, and to new computing paradigms such as the use of multi-core and GPU parallelization. With CORSIKA 8, we have reimplemented the core functionality of CORSIKA in a modern, modular, C++-based simulation framework, and successfully validated it against CORSIKA 7. Here, we discuss the philosophy of CORSIKA 8, showcase some example applications, and present the current state of implementation as well as the plans for the future.
Abstract
Radio waves, perhaps because our terrestrial atmosphere and the cosmos beyond are uniquely transparent to them, or perhaps because they are macroscopic, so the basic instruments of detection ...(antennas) are easily constructible, arguably occupy a privileged position within the electromagnetic spectrum, and, correspondingly, receive disproportionate attention experimentally. Detection of radio-frequency radiation, at macroscopic wavelengths, has blossomed within the last decade as a competitive method for the measurement of cosmic particles, particularly charged cosmic rays and neutrinos. Cosmic-ray detection via radio emission from extensive air showers has been demonstrated to be a reliable technique that has reached a reconstruction quality of the cosmic-ray parameters competitive with more traditional approaches. Radio detection of neutrinos in dense media seems to be the most promising technique to achieve the gigantic detection volumes required to measure neutrinos at energies beyond the PeV-scale flux established by IceCube. In this article, we review radio detection both of cosmic rays in the atmosphere, as well as neutrinos in dense media.
Measuring radio emission from air showers provides excellent opportunities to directly measure all air shower properties, including the shower development. To exploit this in large-scale experiments, ...a simple and analytic parameterization of the distribution of the radio signal at ground level is needed. Data taken with the Low-Frequency Array (LOFAR) show a complex two-dimensional pattern of pulse powers, which is sensitive to the shower geometry. Earlier parameterizations of the lateral signal distribution have proven insufficient to describe these data. In this article, we present a parameterization derived from air-shower simulations. We are able to fit the two-dimensional distribution with a double Gaussian, requiring five fit parameters. All parameters show strong correlations with air shower properties, such as the energy of the shower, the arrival direction, and the shower maximum. We successfully apply the parameterization to data taken with LOFAR and discuss implications for air shower experiments.
A large scientific community depends on the precise modeling of complex processes in particle cascades in various types of matter. These models are used most prevalently in cosmic ray physics, ...astrophysical-neutrino physics, and gamma ray astronomy. In this white paper, we summarize the necessary steps to ensure the evolution and future availability of optimal simulation tools. The purpose of this document is not to act as a strict blueprint for next-generation software, but to provide guidance for the vital aspects of its design. The topics considered here are driven by physics and scientific applications. Furthermore, the main consequences of implementation decisions on performance are outlined. We highlight the computational performance as an important aspect guiding the design, since future scientific applications will heavily depend on an efficient use of computational resources.
The Auger Engineering Radio Array (AERA) complements the Pierre Auger Observatory with 150 radio-antenna stations measuring in the frequency range from 30 to 80 MHz. With an instrumented area of 17 ...km
2
, the array constitutes the largest cosmic-ray radio detector built to date, allowing us to do multi-hybrid measurements of cosmic rays in the energy range of 10
17
eV up to several 10
18
eV. We give an overview of AERA results and discuss the significance of radio detection for the validation of the energy scale of cosmicray detectors as well as for mass-composition measurements.
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