Radio Emission Of Air Showers Research Articles

A new network of electric field mills at the Pierre Auger Observatory

The Pierre Auger Observatory is the largest ground-based experiment for the detection of ultra-high energy cosmic rays. In a hybrid approach, many detectors – including radio antennas – observe the extensive air showers induced by cosmic rays. As part of the AugerPrime upgrade, new antennas will be installed on each of the surface-detector stations covering a total area of around 3000 km2. This will allow us to study the mass composition of cosmic rays arriving with large inclination angles.The radio emission of air showers is heavily influenced in the presence of strong atmospheric electric fields during thunderstorm conditions. In that case measured data are difficult to interpret and therefore the atmospheric electric field over the array has to be monitored. We present the design and status of a new network of electric field mills (EFM) that will be used to take on this task. We show how we plan to perform the measurements with an absolute calibration. In addition, the electric-field data will be useful for other studies related to atmospheric electricity.

Radio Emission of Extensive Air Showers in the Kinetic Model

Radio Emission of Extensive Air Showers in the Kinetic Model

Reconstructing air shower parameters with LOFAR using event specific GDAS atmosphere

The limited knowledge of atmospheric parameters like humidity, pressure, temperature, and the index of refraction has been one of the important systematic uncertainties in reconstructing the depth of the shower maximum from the radio emission of air showers. Current air shower Monte Carlo simulation codes like CORSIKA and the radio plug-in CoREAS use various averaged parameterized atmospheres. However, time-dependent and location-specific atmospheric models are needed for the cosmic ray analysis method used for LOFAR data. There, dedicated simulation sets are used for each detected cosmic ray, to take into account the actual atmospheric conditions at the time of the measurement. Using the Global Data Assimilation System (GDAS), a global atmospheric model, we have implemented time-dependent, realistic atmospheric profiles in CORSIKA and CoREAS. We have produced realistic event-specific atmospheres for all air showers measured with LOFAR, an event set spanning several years and many different weather conditions. A complete re-analysis of our data set shows that for the majority of data, our previous correction factor performed rather well; we found only a small systematic shift of 2 g/cm2 in the reconstructed Xmax. However, under extreme weather conditions, for example, very low air pressure, the shift can be up to 15 g/cm2. We provide a correction formula to determine the shift in Xmax resulting from a comparison of simulations done using the US-Std atmosphere and the GDAS-based atmosphere.

Microscopic approach to the calculation of extensive air shower radio emission

Abstract—Within the kinetic theory of extensive air shower (EAS), an approach to calculating electron charge excess radio emission is formulated. Using the Tamm formula, emission of each electron of the shower disk is calculated taking into account its spatial distribution, temporal evolution along the EAS track, electron energy spectrum, and multiple scattering. Radiation from all EAS tracks is summed taking into account partial coherence loss.

Detector developments for a hybrid particle and radio array for cosmic-ray air-shower detection

Large-scale air-shower arrays could profit from a radio sub-detector as the radio emission in air showers is sensitive to the electromagnetic component. In particular, with an array of radio antennas in combination with particle detectors highly inclined EAS can be detected. This gives rise to new science cases, e.g. the search for PeV gamma rays coming from the Galactic Center at the South Pole, from where it is visible all over the year at an inclination of 61° degree. We report on progress and plans in the development of an optimized hybrid detector.

Current Status and New Challenges of The Tunka Radio Extension

The Tunka Radio Extension (Tunka-Rex) is an antenna array spread over an area of about 1 km2. The array is placed at the Tunka Advanced Instrument for cosmic rays and Gamma Astronomy (TAIGA) and detects the radio emission of air showers in the band of 30 to 80 MHz. During the last years it was shown that a sparse array such as Tunka-Rex is capable of reconstructing the parameters of the primary particle as accurate as the modern instruments. Based on these results we continue developing our data analysis. Our next goal is the reconstruction of cosmic-ray energy spectrum observed only by a radio instrument. Taking a step towards it, we develop a model of aperture of our instrument and test it against hybrid TAIGA observations and Monte-Carlo simulations. In the present work we give an overview of the current status and results for the last five years of operation of Tunka-Rex and discuss prospects of the cosmic-ray energy estimation with sparse radio arrays.

A new parametrization for the radio emission of air showers applied to LOFAR data

The energy and mass composition of cosmic rays influence how the energy density of the radio emission of air showers is distributed on the ground. A precise description of the radio profiles can, therefore, be used to reconstruct the properties of the primary cosmic rays. Here, such a description is presented, using a separate treatment of the two radio-emission mechanisms, the geomagnetic effect and the charge excess effect. The model is parametrized as a function that depends only on the shower parameters, allowing for a precise reconstruction of the properties of the primary cosmic rays. This model is applied to cosmic-ray events measured with LOFAR and it is capable of reconstructing the properties of air showers correctly.

An analytic description of the radio emission of air showers based on its emission mechanisms

The spatial signal distribution of the radio frequency radiation from extensive air showers on the ground contains information on crucial cosmic-ray properties, such as energy and mass. A long-standing challenge to access this information experimentally with a sparse grid of antennas is an analytic modeling of the radio signal distribution, which will be addressed in this contribution. We present an analytic model based on the two physical processes generating radio emission in air showers: the geomagnetic and the charge-excess emission. Our study is based on full Monte-Carlo simulations with the CoREAS code. Besides an improved theoretical understanding of radio emission, our model describes the radio signal distribution with unprecedented precision. Our model explicitly includes polarization information, which basically doubles the information that is used from a single radio station. The model depends only on the definition of the shower axis and on the parameters energy and distance to the emission region, where the distance to the emission region has a direct relation to the cosmic-ray mass. The model describes the true signal distribution precisely such that the model uncertainties are negligible compared to typical experimental uncertainties.

An analytic description of the radio emission of air showers based on its emission mechanisms

Ultra-high energy cosmic rays can be measured through the detection of radio-frequency radiation from air showers. The radio-frequency emission originates from deflections of the air-shower particles in the geomagnetic field and from a time-varying negative charge excess in the shower front. The distribution of the radio signal on the ground contains information on crucial cosmic-ray properties, such as energy and mass. A long standing challenge is to access this information experimentally with a sparse grid of antennas. We present a new analytic model of the radio signal distribution that depends only on the definition of the shower axis and on the parameters energy and distance to the emission region. The distance to the emission region has a direct relation to the cosmic rays mass. This new analytic model describes the different polarizations of the radiation and therefore allows the use of independently measured signals in different polarization, thereby doubling the amount of information that is available in current radio arrays, compared to what has been used thus far. We show with the use of CoREAS Monte Carlo simulation that fitting the measurements with our model does not result in significant contributions in both systematic bias and in resolution for the extracted parameters energy and distance to emission region, when compared to the expected experimental measurement uncertainties. This parametrization also enables fast simulation of radio signal patterns for cosmic rays, without the need to simulate the air shower.

Radio emission of air showers with extremely high energy measured by the Yakutsk Radio Array

The Yakutsk Array is designed to study cosmic rays at energy 1015−1020eV. It consists several independent arrays that register charged particles, muons with energy E≥1GeV, Cherenkov light and radio emission. The paper presents a technical description of the Yakutsk Radio Array and some preliminary results obtained from measurements of radio emission at 30–35 MHz frequency induced by air shower particles with energy ε≥1⋅1017eV. The data obtained at the Yakutsk array in 1986–1989 (first set of measurements) and 2009–2014 (new set of measurements). Based on the obtained results we determined: Lateral distribution function (LDF) of air showers radio emission with energy ≥1017eV. Radio emission amplitude empirical connection with air shower energy. Determination of depth of maximum by ratio of amplitude at different distances from the shower axis. For the first time, at the Yakutsk array radio emission from the air shower with energy >1019eV was registered including the shower with the highest energy ever registered at the Yakutsk array with energy ∼2⋅1020eV.

Radio detection of air showers with the ARIANNA experiment on the Ross Ice Shelf

The ARIANNA hexagonal radio array (HRA) is an experiment in its pilot phase designed to detect cosmogenic neutrinos of energies above 1016 eV. The most neutrino-like background stems from the radio emission of air showers. This article reports on dedicated efforts of simulating and detecting the signals of cosmic rays. A description of the fully radio self-triggered data-set, the properties of the detected air shower signals in the frequency range of 100–500 MHz and the consequences for neutrino detection are given. 38 air shower signals are identified by their distinct waveform characteristics, are in good agreement with simulations and their signals provide evidence that neutrino-induced radio signals will be distinguishable with high efficiency in ARIANNA. The cosmic ray flux at a mean energy of 6.5−1.0+1.2×1017 eV is measured to be 1.1−0.7+1.0×10−16 eV−1 km−2 sr−1 yr−1 and one five-fold coincident event is used to illustrate the capabilities of the ARIANNA detector to reconstruct arrival direction and energy of air showers.

Radio detection of extensive air showers

Radio detection of extensive air showers initiated in the Earth's atmosphere has made tremendous progress in the last decade. Today, radio detection is routinely used in several cosmic-ray observatories. The physics of the radio emission in air showers is well-understood, and analysis techniques have been developed to determine the arrival direction, the energy and an estimate for the mass of the primary particle from the radio measurements. The achieved resolutions are competitive with those of more traditional techniques. In this article, I shortly review the most important achievements and discuss the potential for future applications.

Radio emission of extensive air showers at microwave frequencies

It is found that the power of the incoherent radiation of ionization electrons of an extensive air shower in the frequency range of 150 GHz is more than 10–24 W/m2Hz, with the shower energy ~1018 eV at a distance of 5 km from its axis. This means that, unlike fluorescent detectors, a radio telescope with an effective area of more than 300 m2 can monitor the trajectory of showers with an energy higher than 1018 eV at any time of the day regardless of the weather. The spectrum maximum near the frequency of 150 GHz is roughly three orders of magnitude higher than the value experimentally measured in the characteristic band (~5-10 GHz).

Improved absolute calibration of LOPES measurements and its impact on the comparison with REAS 3.11 and CoREAS simulations

LOPES was a digital antenna array detecting the radio emission of cosmic-ray air showers. The calibration of the absolute amplitude scale of the measurements was done using an external, commercial reference source, which emits a frequency comb with defined amplitudes. Recently, we obtained improved reference values by the manufacturer of the reference source, which significantly changed the absolute calibration of LOPES. We reanalyzed previously published LOPES measurements, studying the impact of the changed calibration. The main effect is an overall decrease of the LOPES amplitude scale by a factor of 2.6 ± 0.2, affecting all previously published values for measurements of the electric-field strength. This results in a major change in the conclusion of the paper ‘Comparing LOPES measurements of air-shower radio emission with REAS 3.11 and CoREAS simulations’ published by Apel et al. (2013) : With the revised calibration, LOPES measurements now are compatible with CoREAS simulations, but in tension with REAS 3.11 simulations. Since CoREAS is the latest version of the simulation code incorporating the current state of knowledge on the radio emission of air showers, this new result indicates that the absolute amplitude prediction of current simulations now is in agreement with experimental data.

The radio emission pattern of air showers as measured with LOFAR—a tool for the reconstruction of the energy and the shower maximum

The pattern of the radio emission of air showers is finely sampled with the Low-Frequency ARray (LOFAR). A set of 382 measured air showers is used to test a fast, analytic parameterization of the distribution of pulse powers. Using this parameterization we are able to reconstruct the shower axis and give estimators for the energy of the air shower as well as the distance to the shower maximum.

Evidence for the charge-excess contribution in air shower radio emission observed by the CODALEMA experiment

CODALEMA is one of the pioneer experiments dedicated to the radio detection of ultra high energy cosmic rays (UHECR), located at the radio observatory of Nançay (France). The CODALEMA experiment uses both a particle detector array and a radio antenna array. Data from both detection systems have been used to determine the ground coordinates of the core of extensive air showers (EAS). We discuss the observed systematic shift of the core positions determined with these two detection techniques. We show that this shift is due to the charge-excess contribution to the total radio emission of air showers, using the simulation code SELFAS. The dependences of the radio core shift to the primary cosmic ray characteristics are studied in details. The observation of this systematic shift can be considered as an experimental signature of the charge excess contribution.

Радиоизлучение широких атмосферных ливней

Радиоизлучение широких атмосферных ливней

Measuring a Cherenkov ring in the radio emission from air showers at 110–190 MHz with LOFAR

Measuring radio emission from air showers offers a novel way to determine properties of the primary cosmic rays such as their mass and energy. Theory predicts that relativistic time compression effects lead to a ring of amplified emission which starts to dominate the emission pattern for frequencies above ∼100MHz. In this article we present the first detailed measurements of this structure. Ring structures in the radio emission of air showers are measured with the LOFAR radio telescope in the frequency range of 110–190MHz. These data are well described by CoREAS simulations. They clearly confirm the importance of including the index of refraction of air as a function of height. Furthermore, the presence of the Cherenkov ring offers the possibility for a geometrical measurement of the depth of shower maximum, which in turn depends on the mass of the primary particle.

A parameterization for the radio emission of air showers as predicted by CoREAS simulations and applied to LOFAR measurements

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.

Recent results from cosmic-ray measurements with LOFAR

LOFAR, the Low Frequency Array, is currently the world's largest distributed radio telescope observing at frequencies below 240MHz. LOFAR is measuring cosmic-ray induced air-showers since June 2011 and has collected several hundreds of events with hundreds of antennas per individual event. We present measurements of the radio signal strength as well as high-precision measurements of wavefront curvature and polarization. These will enable us to disentangle the different emission mechanisms at play, such as geomagnetic radiation, charge excess, and Askaryan or Cherenkov effects, leading to a full understanding of the air-shower radio emission. Furthermore we give a first example on how the full complexity of the signal enables radio measurements to be used to study primary particle composition.