Search

The hardness of the energy spectrum of neutral pions produced in proton-air interactions at ultra-high energies, above 1018 eV, is constrained by the steepness of the shower-to-shower distribution of the number of muons in muon-depleted extensive air showers.In this work, we find that this steepness, quantified by the parameter Λμ, evolves with the depth of the shower maximum, Xmax, assuming a universal value for shallow showers and an enhanced dependence on the high-energy hadronic interaction model for deep showers. We show that Xmax probes the so-called hadronic activity of the first proton-air interaction, thus allowing direct access to the energy spectrum of neutral pions in different regions of its kinematic phase space.We verify that the unbiased measurement of Λμ is possible for realistic mass composition expectations. Finally, we infer that the statistical precision in Λμ required to distinguish between hadronic interaction models can be achieved in current extensive air shower detectors, given their resolution and exposure.

The hardness of the energy spectrum of neutral pions produced in proton-air interactions at ultra-high energies, above 1018 eV, is constrained by the steepness of the shower-to-shower distribution of the number of muons in muon-depleted extensive air showers. In this work, we find that this steepness, quantified by the parameter Λ μ , evolves with the depth of the shower maximum, X max , assuming a universal value for shallow showers and an enhanced dependence on the high-energy hadronic interaction model for deep showers. We show that X max probes the so-called hadronic activity of the first proton-air interaction, thus allowing direct access to the energy spectrum of neutral pions in different regions of its kinematic phase space. We verify that the unbiased measurement of Λ μ is possible for realistic mass composition expectations. Finally, we infer that the statistical precision in Λ μ required to distinguish between hadronic interaction models can be achieved in current extensive air shower detectors, given their resolution and exposure. [ABSTRACT FROM AUTHOR]

The Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) is a proposed dual-satellite mission to observe Ultra-High-Energy Cosmic Rays (UHECRs), increasing the statistics at the highest energies, and Very-High-Energy Neutrinos (VHENs), following multi-messenger alerts of astrophysical transient events throughout the universe such as gamma-ray bursts and gravitational wave events. POEMMA-Balloon with Radio (PBR) is a scaled-down version of the POEMMA design, adapted to be flown as a payload on one of NASA's sub-orbital Super Pressure Balloons (SPBs) circling over the Southern Ocean for up to 100 days after a launch from Wanaka, New Zealand. This overview will provide a summary of the mission with its science goals, the instruments, and the current status of PBR. [ABSTRACT FROM AUTHOR]

In this paper, I present a qualitative discussion on the prospect of production of ultra-high photons in blazars. The sources are a subclass of active galactic nuclei which host supermassive black holes and fire relativistic jets into the intergalactic medium. The kpc-scale jets are believed to be dominated by Poynting flux and constitute one of the most efficient cosmic particle accelerators, that potentially are capable of accelerating the particles up to EeV energies. Recent IceCube detection of astrophysical neutrino emissions, in coincidence with the enhanced gamma-ray from Tev blazar TXS 0506 + 056, further supports hadronic models of blazar emissions in which particle acceleration processes, such as relativistic shocks, magnetic re-connection, and relativistic turbulence, could energize hadrons, e.g., protons, up to energies equivalent to billions of Lorentz factors. The ensuing photo-pionic processes may then result in gamma-rays accompanied by neutrino flux. Furthermore, the fact that blazars are the dominant source of observed TeV emission encourages search for signatures of acceleration scenarios that would lead to the creation of ultra-high-energy photons. [ABSTRACT FROM AUTHOR]

The source, origin, and acceleration mechanisms of ultra-high-energy cosmic rays (UHECR) ( E > 10 20 eV, beyond the GZK limit) remain uncertain and unclear. The main explanations are associated with particular mechanisms, such as the Fermi mechanism, in which charged particles could be accelerated by clouds of magnetized gas moving within our Galaxy, or by the magnetic reconnection of field lines at, e.g., the core of high-energy astrophysical sources, where the topology of the magnetic field is rearranged and magnetic energy is converted into kinetic energy. However, the recent observation of extragalactic neutrinos may suggest that the source of UHECRs is likely an extragalactic supermassive black hole. In the present work, we propose that charged particles can be accelerated to ultrahigh energies in marginally bound orbits near extreme rotating black holes and could be triggered by collisions of magnetocentrifugal winds; the accretion disk surrounding the black hole would provide such winds. The ultra-high-energy process is governed by the frame-dragging effects of the black hole spacetime. [ABSTRACT FROM AUTHOR]

We review the peculiarities that make neutrinos very special cosmic messengers in high-energy astrophysics, and, in particular, to provide possible indications of deviations from special relativity, as it is suggested theoretically by quantum gravity models. In this respect, we examine the effects that one could expect in the production, propagation, and detection of neutrinos, not only in the well-studied scenario of Lorentz Invariance Violation, but also in models which maintain, but deform, the relativity principle, such as those considered in the framework of Doubly Special Relativity. We discuss the challenges and the promising future prospects offered by this phenomenological window to physics beyond special relativity. [ABSTRACT FROM AUTHOR]

Interactions of ultra-high energy cosmic-rays (UHECRs) accelerated in astrophysical environments have been shown to shape the energy production rate of nuclei escaping from the confinement zone. To address the influence of hadronic interactions, Hadronic Interaction Models (HIMs) come into play. In this context, we present a parameterization capable of capturing the outcomes of two distinct HIMs, namely EPOS-LHC and Sibyll2.3d, in terms of secondary fluxes, including escaping nuclei, nucleons, neutrinos, photons, and electrons. Our parameterization is systematically evaluated against the source codes, both at fixed energy and mass, as well as in a physical case scenario. The comparison demonstrates that our parameterization aligns well with the source codes, establishing its reliability as a viable alternative for analytical or fast Monte Carlo approaches dedicated to the study of UHECR propagation within source environments. This suggests the potential for utilizing our parameterization as a practical substitute in studies focused on the intricate dynamics of ultra-high energy cosmic rays. [ABSTRACT FROM AUTHOR]

In this paper, I present a qualitative discussion on the prospect of production of ultra-high photons in blazars. The sources are a subclass of active galactic nuclei which host supermassive black holes and fire relativistic jets into the intergalactic medium. The kpc-scale jets are believed to be dominated by Poynting flux and constitute one of the most efficient cosmic particle accelerators, that potentially are capable of accelerating the particles up to EeV energies. Recent IceCube detection of astrophysical neutrino emissions, in coincidence with the enhanced gamma-ray from Tev blazar TXS 0506 + 056, further supports hadronic models of blazar emissions in which particle acceleration processes, such as relativistic shocks, magnetic re-connection, and relativistic turbulence, could energize hadrons, e.g., protons, up to energies equivalent to billions of Lorentz factors. The ensuing photo-pionic processes may then result in gamma-rays accompanied by neutrino flux. Furthermore, the fact that blazars are the dominant source of observed TeV emission encourages search for signatures of acceleration scenarios that would lead to the creation of ultra-high-energy photons.

One of the most captivating problems being faced nowadays in Physics are ultra-high energy cosmic rays. They are high-energy radiations coming mainly from outside the Solar System, and when they enter Earth's atmosphere, they produce a cascade of particles. This cascade of particles, named as extensive air shower, can be recorded by means of photomultiplier tubes in surface detectors, obtaining different recordings of the energy signal (since the air shower can hit one or more detectors). Based on these signals, different features can be obtained that might give an insight into which particle has caused the extensive air shower, which is of utmost importance for physicists. Therefore, this work presents a supervised learning algorithm to determine that the particle is a photon or a hadron. Convolutional neural networks and feed forward neural networks are compared in order to analyze the importance of spatial information for the classification. Then, a comparison between using the information of each surface detector separately and integrating the information from them for the classification is studied, showing that the integration improves the results compared to using each surface detector's trace independently. Furthermore, a comparison between manually extracted features from the signal and the automatically extracted features by the convolutional neural network is done, showing the classification potential of the latter. Finally, the addition of particle shower features which are external to the surface detector measurements is assessed, showing that the combination of automatically extracted features and external variables is able to predict the particle that has produced the air shower with an accuracy of 98.87%. [ABSTRACT FROM AUTHOR]

The source, origin, and acceleration mechanisms of ultra-high-energy cosmic rays (UHECR) (E>1020 eV, beyond the GZK limit) remain uncertain and unclear. The main explanations are associated with particular mechanisms, such as the Fermi mechanism, in which charged particles could be accelerated by clouds of magnetized gas moving within our Galaxy, or by the magnetic reconnection of field lines at, e.g., the core of high-energy astrophysical sources, where the topology of the magnetic field is rearranged and magnetic energy is converted into kinetic energy. However, the recent observation of extragalactic neutrinos may suggest that the source of UHECRs is likely an extragalactic supermassive black hole. In the present work, we propose that charged particles can be accelerated to ultrahigh energies in marginally bound orbits near extreme rotating black holes and could be triggered by collisions of magnetocentrifugal winds; the accretion disk surrounding the black hole would provide such winds. The ultra-high-energy process is governed by the frame-dragging effects of the black hole spacetime.

We review the peculiarities that make neutrinos very special cosmic messengers in high-energy astrophysics, and, in particular, to provide possible indications of deviations from special relativity, as it is suggested theoretically by quantum gravity models. In this respect, we examine the effects that one could expect in the production, propagation, and detection of neutrinos, not only in the well-studied scenario of Lorentz Invariance Violation, but also in models which maintain, but deform, the relativity principle, such as those considered in the framework of Doubly Special Relativity. We discuss the challenges and the promising future prospects offered by this phenomenological window to physics beyond special relativity.

Radio-detection is becoming an established technique for the detection of air showers induced by cosmic particles. This is in particular true at the highest energies, where very large detection areas are required. A proper description of the shape of the radio wavefront emitted by air showers may allow to reconstruct the properties of its parent particle. In this article, we show that for showers with zenith angles larger than 60 ° – those targeted by giant radio arrays detecting extensive air showers induced by cosmic particles –, a point-source-like description of the radio wavefront allows to constraint the lateral position of the shower axis within a few meters. Following, we show that the reconstructed longitudinal position of this point source is correlated with the nature of the cosmic rays initiating the shower. Further systematic studies are pending to determine the robustness of this parameter and its validity as a proxy for cosmic ray composition studies. [ABSTRACT FROM AUTHOR]

Various experiments have been conducted to search for the radio emission from ultra-high-energy (UHE) particles interacting in the lunar regolith. Although they have not yielded any detections, they have been successful in establishing upper limits on the flux of these particles. I present a review of these experiments in which I re-evaluate their sensitivity to radio pulses, accounting for effects which were neglected in the original reports, and compare them with prospective near-future experiments. In several cases, I find that past experiments were substantially less sensitive than previously believed. I apply existing analytic models to determine the resulting limits on the fluxes of UHE neutrinos and cosmic rays (CRs). In the latter case, I amend the model to accurately reflect the fraction of the primary particle energy which manifests in the resulting particle cascade, resulting in a substantial improvement in the estimated sensitivity to CRs. Although these models are in need of further refinement, in particular to incorporate the effects of small-scale lunar surface roughness, their application here indicates that a proposed experiment with the LOFAR telescope would test predictions of the neutrino flux from exotic-physics models, and an experiment with a phased-array feed on a large single-dish telescope such as the Parkes radio telescope would allow the first detection of CRs with this technique, with an expected rate of one detection per 140 h. [ABSTRACT FROM AUTHOR]

We describe an experiment using the Parkes radio telescope in the 1.2–1.5 GHz frequency range as part of the LUNASKA project, to search for nanosecond-scale pulses from particle cascades in the Moon, which may be triggered by ultra-high-energy astroparticles. Through the combination of a highly sensitive multi-beam radio receiver, a purpose-built backend and sophisticated signal-processing techniques, we achieve sensitivity to radio pulses with a threshold electric field strength of 0.0053 μ V/m/MHz, lower than previous experiments by a factor of three. We observe no pulses in excess of this threshold in observations with an effective duration of 127 h. The techniques we employ, including compensating for the phase, dispersion and spectrum of the expected pulse, are relevant for future lunar radio experiments. [ABSTRACT FROM AUTHOR]

The Telescope Array (TA) is the largest experiment in the Northern Hemisphere currently studying the origin and nature of ultra-high-energy cosmic rays above ∼10 eV by measuring their energy spectrum, mass composition, and arrival directions. It is located in the western desert of central Utah, USA. The TA detector consists of a surface array of 507 scintillation counters, deployed on a square grid of 1.2-km spacing that covers approximately 700 km, and 38 fluorescence telescopes located at three sites looking over the surface array. The TA commenced hybrid observation with both sets of detectors in 2008. Here, we present recent results from these 5 years of data and outline our ongoing and near future plans. [ABSTRACT FROM AUTHOR]

Abstract: The absolute value of the air-fluorescence yield is a key parameter for the energy reconstruction of extensive air showers registered by fluorescence telescopes. In previous publications, we reported a detailed Monte Carlo simulation of the air-fluorescence generation that allowed the theoretical evaluation of this parameter. This simulation has been upgraded in the present work. As a result, we determined an updated absolute value of the fluorescence yield of ph/MeV for the band at 337nm in dry air at 800hPa and 293K, in agreement with experimental values. We have also performed a critical analysis of available absolute measurements of the fluorescence yield with the assistance of our simulation. Corrections have been applied to some measurements to account for a bias in the evaluation of the energy deposition. Possible effects of other experimental aspects have also been discussed. From this analysis, we determined an average fluorescence yield of ph/MeV at the above conditions. [Copyright &y& Elsevier]

In this paper we analyse the energy content of ultra-high-energy cosmic rays (UHECRs), and compare this to the experimental result of the energy recorded of the “Oh-my-God” particle in Utah, October 1991, and, using classical Newtonian mechanics, we approximate a value for the velocity of the particle. Given the relativistic velocity of the particle, we use Special Relativity (S. R.) to explain to what extent time dilation affected the particle, and we investigate how it was possible for the proton's energy to tend towards the Greisen-Zatsepin-Kuzmin (GZK) limit. Furthermore, we investigate the possibility of this occurrence being a hint towards the multi-dimensional Universe suggestions of M-theory, due to its velocities which are simply too high for an Einsteinian four-dimensional spacetime. [ABSTRACT FROM PUBLISHER]

We study the anisotropy in the arrival directions of Pierre Auger Observatory (PAO) ultra-high-energy cosmic rays (UHECRs), using the point source correlational angular distance distribution (CADD). The result shows that the anisotropy is characterized by one prominent excess region and one void region. The excess region is located near the Centaurus A direction, supporting that the Centaurus A is a promising UHECR source. The void region near the south pole direction may be used to limit the diffuse isotropic background contribution. [ABSTRACT FROM AUTHOR]

Abstract: The cosmic ray source spectrum produced by AGN (active galactic nucleus) jets is calculated. A distinctive feature of these calculations is the account for the jet distribution on kinetic energy. The expected cosmic ray spectrum at the Earth is determined with the use of a simple numerical code which takes into account interactions of ultra-high energy protons and nuclei with the background radiation in an expanding universe. [Copyright &y& Elsevier]

Abstract: The CODALEMA experiment aims to study the radio-detection of Ultra High Energy Cosmic Rays in the energy range of 1017 eV. Spread over an area of 0.25km2, the original device hosted at Nançay (France) has mainly benefited of an array of short dipoles, connected by cables up to a centralized acquisition room. Since 2010, a major evolution has been initiated to add 60 autonomous radio-detection stations, covering a surface of 1.5km2. This enlarged configuration should help refine the studies and serve as a bench test for the mastery of autonomous detection. The main characteristics of this new mode of operation is presented in the light of recent results obtained by the original CODALEMA setup. [Copyright &y& Elsevier]

Abstract: Recent results from the Pierre Auger Observatory (PAO) indicate that the composition of ultra-high-energy cosmic rays (UHECRs) with energies above 1019 eV may be dominated by heavy nuclei. An important question is whether the distribution of arrival directions for such UHECR nuclei can exhibit observable anisotropy or positional correlations with their astrophysical source objects despite the expected strong deflections by intervening magnetic fields. For this purpose, we have simulated the propagation of UHECR nuclei including models for both the extragalactic magnetic field (EGMF) and the Galactic magnetic field (GMF). We find that the GMF is particularly crucial for suppressing the anisotropy as well as source correlations. Assuming that only iron nuclei are injected steadily from sources with equal luminosity and spatially distributed according to the observed large scale structure in the local Universe, at the number of events published by the PAO so far (69 events above 5.5×1019 eV), the arrival distribution of UHECRs would be consistent with no auto-correlation at 95% confidence if the mean number density of UHECR sources n s ≳10−6 Mpc−3, and consistent with no cross-correlation with sources within 95% errors for n s ≳10−5 Mpc−3. On the other hand, with 1000 events above 5.5×1019 eV in the whole sky, next generation experiments can reveal auto-correlation with more than 99% probability even for n s ≲10−3 Mpc−3, and cross-correlation with sources with more than 99% probability for n s ≲10−4 Mpc−3. In addition, we find that the contribution of Centaurus A is required to reproduce the currently observed UHECR excess in the Centaurus region. Secondary protons generated by photodisintegration of primary heavy nuclei during propagation play a crucial role in all cases, and the resulting anisotropy at small angular scales should provide a strong hint of the source location if the maximum energies of the heavy nuclei are sufficiently high. [Copyright &y& Elsevier]

Abstract: The determination of the primary energy and mass of ultra-high-energy cosmic-rays (UHECR) generating extensive air-showers in the Earth’s atmosphere, relies on the detailed modeling of hadronic multiparticle production at center-of-mass (c.m.) collision energies up to two orders of magnitude higher than those studied at particle colliders. The first Large Hadron Collider (LHC) data have extended by more than a factor of three the c.m. energies in which we have direct proton–proton measurements available to compare to hadronic models. In this work we compare LHC results on inclusive particle production at energies , and 7TeV to predictions of various hadronic Monte Carlo (MC) models used commonly in cosmic-ray (CR) physics (qgsjet, epos and sibyll). As a benchmark with a standard collider physics model we also show pythia (and phojet) predictions with various parameter settings. While reasonable overall agreement is found for some of the MC, none of them reproduces consistently the evolution of all the observables. We discuss implications of the new LHC data for the description of cosmic-ray interactions at the highest energies. [Copyright &y& Elsevier]

Abstract: Powerful radio-loud active galactic nuclei (AGN) with large Mpc-scale jets have been theoretically motivated as emitters of high-energy cosmic rays. Recent radio observations have established a populous class of young radio-loud galaxies with compact (<1kpc) symmetric jets that are morphologically similar to large-scale AGNs. We show that these compact AGNs, so-called compact symmetric objects (CSOs), can accelerate protons up to 1020 eV at their hot spots via a Fermi type mechanism on the assumption of efficient acceleration. The required magnetic field strengths are comparable to those derived from the minimum energy condition. We further show that the accelerated protons can escape through the photon fields of the cocoon without significant energy loss. However, the local number density of powerful CSOs is insufficient for CSOs to power the entire observed flux of ultra-high-energy cosmic rays, providing maximally only a few percent. A heavy composition of UHECRs allows more CSOs to accelerate particles to UHECR energies, but escaping the cocoon is difficult. We comment on a method that may test CSOs as UHECR sources. [Copyright &y& Elsevier]

Abstract: We have investigated the fluorescence emission in the near infrared from the air and its main components, nitrogen and oxygen. The gas was excited by a 95kV electron beam and the fluorescence light detected by an InGaAs photodiode, sensitive down to about 1700nm. We have recorded the emission spectra by means of a Fourier Transform Infrared spectrometer. The light yield was also measured by comparing the near infrared signal with the known ultraviolet fluorescence, detected by a Si photodiode. The possibility of using the near infrared fluorescence of the atmosphere to detect ultra-high-energy cosmic rays is discussed, showing the pros and the cons of this novel method. [Copyright &y& Elsevier]

We analyze the active-galaxy correlation reported in 2007 by the Pierre Auger Collaboration. The signal diminishes if the correlation-function approach (counting all "source–event" pairs and not only "nearest neighbors") is used, suggesting that the correlation may reveal individual sources and not their population. We analyze available data on physical conditions in these individual correlated sources and conclude that acceleration of protons to the observed energies is hardly possible in any of these galaxies, while heavier nuclei would be deflected by the Galactic magnetic field thus spoiling the correlation. Our results question the Auger interpretation of the reported anisotropy signal but do not contradict to its explanation with intermediate-mass nuclei accelerated in Cen A. [ABSTRACT FROM AUTHOR]

Abstract: Using a large set of simulated extensive air showers, we investigate universality features of electron and positron distributions in very-high-energy cosmic-ray air showers. Most particle distributions depend only on the depth of the shower maximum and the number of particles in the cascade at this depth. We provide multi-dimensional parameterizations for the electron–positron distributions in terms of particle energy, vertical and horizontal momentum angle, lateral distance, and time distribution of the shower front. These parameterizations can be used to obtain realistic electron–positron distributions in extensive air showers for data analysis and simulations of Cherenkov radiation, fluorescence signal, and radio emission. [Copyright &y& Elsevier]

Abstract: There are two promising scenarios that explain the ankle, which is a dip in the spectrum of cosmic rays at eV. A scenario interprets the ankle as the transition from Galactic to extragalactic cosmic rays (ankle-transition scenario), while the other is that the dip is caused by pair production on the cosmic microwave background radiation (proton-dip scenario). In this paper, we considered whether cosmogenic neutrinos can be a clue to judge which scenario is favored. We calculated the fluxes of cosmogenic neutrinos following these scenarios with plausible physical parameter sets, and found several important features as follows. First of all, the neutrino flux at eV becomes much higher in the ankle-transition scenario as long as the maximum energy of the cosmic rays at sources is sufficiently high. On the other hand, the neutrino spectrum has a characteristic peak at eV in the proton-dip scenario on the condition that extragalactic protons significantly contribute to the observed cosmic rays down to eV. Thus, we concluded cosmogenic neutrinos should give us a clue to judge which scenario is favored, unless these features are masked by the neutrino background coming from possible, powerful neutrino sources such as active galactic nuclei and γ-ray bursts. We also found an interesting feature that the neutrino flux at eV depends only on the cosmological evolution of the cosmic ray sources. That means cosmogenic neutrinos with the energy bring us information on the cosmological evolution of the sources of ultra-high energy cosmic rays. Finally, we compared the fluxes of cosmogenic neutrinos with the expected sensitivity curves of several neutrino detectors, and conclude the detection of cosmogenic neutrinos in the near future is promising. [Copyright &y& Elsevier]

Abstract: We estimate the local number density of sources of ultra-high-energy cosmic rays (UHECRs) based on the statistical features of their arrival direction distribution. We calculate the arrival distributions of protons above 1019 eV taking into account their propagation process in the Galactic magnetic field and a structured intergalactic magnetic field, and statistically compare those with the observational results of the Pierre Auger Observatory. The anisotropy in the arrival distribution at the highest energies enables us to estimate the number density of UHECR sources as ∼10−4 Mpc−3 assuming the persistent activity of UHECR sources. We compare the estimated number density of UHECR sources with the number densities of known astrophysical objects. This estimated number density is consistent with the number density of Fanaroff–Reily I galaxies. We also discuss the reproducibility of the observed isotropy in the arrival distribution above 1019 eV. We find that the estimated source model cannot reproduce the observed isotropy. However, the observed isotropy can be reproduced with the number density of . This fact indicates the existence of UHECR sources with a maximum acceleration energy of ∼1019 eV whose number density is an order of magnitude more than that injecting the highest energy cosmic rays. [Copyright &y& Elsevier]

Abstract: We discuss the possibility of accurately estimating the source number density of ultra-high-energy cosmic rays (UHECRs) using small-scale anisotropy in their arrival distribution. The arrival distribution has information on their source and source distribution. We calculate the propagation of UHE protons in a structured extragalactic magnetic field (EGMF) and simulate their arrival distribution at the Earth using our previously developed method. The source number density that can best reproduce observational results by Akeno Giant Air Shower Array is estimated at about 10−5 Mpc−3 in a simple source model. Despite having large uncertainties of about one order of magnitude, due to small number of observed events in current status, we find that more detection of UHECRs in the Auger era can sufficiently decrease this so that the source number density can be more robustly estimated. Two hundred event observation above 4×1019 eV in a hemisphere can discriminate between 10−5 and 10−6 Mpc−3. Number of events to discriminate between 10−4 and 10−5 Mpc−3 is dependent on EGMF strength. We also discuss the same in another source model in this paper. [Copyright &y& Elsevier]

Abstract: Based on a new approach to the detection of radio transients associated with extensive air showers induced by ultra-high-energy cosmic rays, the experimental apparatus CODALEMA is in operation, measuring about 1 event per day corresponding to an energy threshold ∼5×1016 eV. Its performance makes possible for the first time the study of radio-signal features on an event-by-event basis. The sampling of the magnitude of the electric field along a 600m axis is analyzed. It shows that the electric field lateral spread is around 250m (FWHM). The possibility to determine with radio both arrival directions and shower core positions is discussed. [Copyright &y& Elsevier]

Abstract: Corrections for the deflection of charged cosmic-ray particles by the regular component of the Galactic magnetic field (GMF) destroy the ultra-high-energy cosmic-ray clusters observed by the AGASA and Yakutsk experiments, as well as the cluster of five cosmic rays observed by the AGASA, HiRes and Yakutsk experiments, for any of conventional GMF models. This may mean that either the clusters are accidental, or the clustered cosmic rays have neutral primaries, or the GMF models do not work. Assuming the latter possibility, we study the fiveplet in more detail and find which deflections would not destroy the cluster and possibly make it tighter. For different primary charges, we discuss possible astrophysical sources of the particles forming the fiveplet. [Copyright &y& Elsevier]

Abstract: Taking advantage of recent technical progress which has overcome some of the difficulties encountered in the 1960s in the radio detection of extensive air showers induced by ultra-high-energy cosmic rays (UHECR), a new experimental apparatus (CODALEMA) has been built and operated. We will present the characteristics of this device and the analysis techniques that have been developed for observing electrical transients associated with cosmic rays. We find a collection of events for which both time and arrival direction coincidences between particle and radio signals are observed. The counting rate corresponds to shower energies . The performance level which has been reached considerably enlarges the perspectives for studying UHECR events using radio detection. [Copyright &y& Elsevier]

Abstract: The space optical detectors of ultra-high-energy cosmic rays, aimed for detection of the fluorescence light radiated by the EAS particle disc, may also register the Cherenkov light scattered in the atmosphere and diffused by the clouds, ground or sea. The diffused Cherenkov signal gives the reference height in the atmosphere needed for the measurement of the EAS maximum position. [Copyright &y& Elsevier]