Autonomous radio-detection, i.e., detection of air-showers with standalone radio arrays, is one of the major technical challenges to overcome for the next generation astroparticle detectors. In this ...context, we study polarisation signatures of simulated radio signals to perform an identification of the associated air-showers initiated by cosmic-rays and neutrinos. We compare the two sources of radio emission (the charge excess and geomagnetic) and show that the former is almost negligible for inclined (zenith angle >65°) cosmic-ray air-showers. This provides an efficient background rejection criterion at the DAQ level, based on the projection of the total electric field along the direction of the local magnetic field. This relevant quantity can be computed, — even in an online treatment — for antennas measuring three orthogonal polarisations. Independently of the experimental antenna layout, we estimate that assuming a random polarisation of noise events, a rejection from ≈72% (for a non favourable detector location) to ≈93% (for a favourable one) of the noise induced events and a trigger efficiency of 86% (93%) with a 3σ (5σ) trigger threshold level should be achievable. We also show that neutrino-induced showers present a charge excess to geomagnetic signal ratio up to ∼10 times higher than for cosmic ray showers. Although this characteristic makes the identification of neutrino-induced showers challenging via the method developed here, it provides an efficient criterion to perform an offline discrimination between cosmic-ray and neutrino primaries. The stronger charge excess emission will also help the reconstruction of air-shower parameters, such as the core position.
Over the last years, radio detection has matured to become a competitive method for the detection of air showers. Arrays of thousands of antennas are now envisioned for the detection of cosmic rays ...of ultra high energy or neutrinos of astrophysical origin. The data exploitation of such detectors requires to run massive air-shower simulations to evaluate the radio signal at each antenna position. In order to reduce the associated computational cost, we have developed a semi-analytical method for the computation of the emitted radio signal called Radio Morphing. The method consists in computing the radio signal of any air-shower at any location from the simulation of one single reference shower at given positions by (i) a scaling of the electric-field amplitude of this reference shower, (ii) an isometry on the simulated positions and (iii) an interpolation of the radio pulse at the desired position. This technique enables one to compute electric field time traces with characteristics very similar to those obtained with standard computation methods, but with computation times reduced by several orders of magnitude. In this paper, we present this novel tool, explain its methodology, and discuss its limitations. Furthermore, we validate the method on a typical event set for the future GRAND experiment showing that the calculated peak amplitudes are consistent with the results from ZHAireS simulations with a mean offset of +8.5% and a standard deviation of 27.2% in this specific case. This overestimation of the signal strength by Radio Morphing arises mainly from the choice of the underlying reference shower.
An ultra-high-energy cosmic ray (UHECR) colliding with the Earth's atmosphere gives rise to an Extensive Air Shower (EAS). Due to different charge separation mechanisms within the thin shower front ...coherent electromagnetic radiation will be emitted within the radio frequency range. A small deviation of the index of refraction from unity will give rise to Cherenkov radiation up to distances of 100
m from the shower core and therefore has to be included in a complete description of the radio emission from an EAS. Interference between the different radiation mechanisms, in combination with different polarization behavior will reflect in a lateral distribution function (LDF) depending on the orientation of the observer and a non-trivial fall-off of the radio signal as function of distance to the shower core.
Abstract
We recently reported on the radio-frequency attenuation length of cold polar ice at Summit Station, Greenland, based on bi-static radar measurements of radio-frequency bedrock echo strengths ...taken during the summer of 2021. Those data also allow studies of (a) the relative contributions of coherent (such as discrete internal conducting layers with sub-centimeter transverse scale) vs incoherent (e.g. bulk volumetric) scattering, (b) the magnitude of internal layer reflection coefficients, (c) limits on signal propagation velocity asymmetries (‘birefringence’) and (d) limits on signal dispersion in-ice over a bandwidth of ~100 MHz. We find that (1) attenuation lengths approach 1 km in our band, (2) after averaging 10 000 echo triggers, reflected signals observable over the thermal floor (to depths of ~1500 m) are consistent with being entirely coherent, (3) internal layer reflectivities are ≈–60
$\to$
–70 dB, (4) birefringent effects for vertically propagating signals are smaller by an order of magnitude relative to South Pole and (5) within our experimental limits, glacial ice is non-dispersive over the frequency band relevant for neutrino detection experiments.
Coherent radiation from extensive air showers Scholten, Olaf; de Vries, Krijn D.; Werner, Klaus
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
2012, Letnik:
662
Journal Article
Recenzirano
Odprti dostop
The generic properties of the emission of coherent radiation from a moving charge distribution are discussed. The general structure of the charge and current distributions in an extensive air shower ...are derived. These are subsequently used to develop a very intuitive picture for the properties of the emitted radio pulse. Using this picture can be seen that the structure of the pulse is a direct reflection of the shower profile. At higher frequencies the emission is suppressed because the wavelength is shorter than the important length scale in the shower. It is shown that radio emission can be used to distinguish proton- and iron-induced air showers.
The lateral distribution function (LDF) for coherent electromagnetic radiation from air showers initiated by ultra-high-energy cosmic rays is calculated using a macroscopic description. A new ...expression is derived to calculate the coherent radio pulse at small distances from the observer. It is shown that for small distances to the shower axis the shape of the electric pulse is determined by the 'pancake' function, describing the longitudinal distribution of charged particles within the shower front, while for large distances the pulse is determined by the shower profile. This reflects in a different scaling of the LDF at small and at large distances. As a first application we calculate the LDF for proton- and iron-induced showers and we show that this offers a very sensitive measure to discriminate between these two. We show that due to interference between the geo-magnetic and the charge-excess contributions the intensity pattern of the radiation is not circular symmetric.
We explore the possibility that the astrophysical neutrinos are produced in
$pp$-interactions with a gas cloud near the source acting as a beam dump, which
is sufficiently dense to significantly ...attenuate the associated gamma-ray flux
through pair-production on this gas. In this way, such sources could
potentially supply the astrophysical neutrino flux whilst avoiding the existing
constraints on the non-blazar contribution to the extragalactic gamma-ray
background. After defining our model, we implement a Monte Carlo simulation and
apply this to different scenarios. First, we investigate a set of active
galaxies which exhibit signs of obscuration. We find that, currently, the
expected neutrino flux from these objects in our model is below the existing
exclusion limits, but can already constrain the amount of protons accelerated
in such sources. Second, we investigate the diffuse neutrino flux generated by
a population of obscured sources. We find that such a population can indeed
alleviate the tension with the extragalactic background light. We discuss the
possibility that ultra-luminous infrared galaxies represent such a source
class.
We present detailed microscopic simulations of high-energy cosmic-ray air showers penetrating high-altitude ice layers that can be found at the polar regions. We use a combination of the CORSIKA ...Monte Carlo code and the Geant4 simulation toolkit, and focus on the particle cascade that develops in the ice to describe its most prominent features. We discuss the impact of the ice layer on the total number of particles in function of depth of the air shower, and we give a general parameterization of the charge distribution in the cascade front in function of Xmax of the cosmic ray air shower, which can be used for analytical and semi-analytical calculations of the expected Askaryan radio emission of the in-ice particle cascade. We show that the core of the cosmic ray air shower dominates during the propagation in ice, therefore creating an in-ice particle cascade strongly resembling a neutrino-induced particle cascade. Finally, we present the results of microscopic simulations of the Askaryan radio emission of the in-ice particle cascade, showing that the emission is dominated by the shower core, and discuss the feasibility of detecting the plasma created by the particle cascade in the ice using RADAR echo techniques.
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