Ground-based gamma-ray astronomy aims at reconstructing the energy and direction of gamma rays from the extensive air showers they initiate in the atmosphere. Imaging Atmospheric Cherenkov Telescopes (IACT) collect the Cherenkov light induced by secondary charged particles in extensive air showers (EAS), creating an image of the shower in a camera positioned in the focal plane of optical systems. This image is used to evaluate the type, energy and arrival direction of the primary particle that initiated the shower. This contribution shows the results of a novel reconstruction method based on likelihood maximization. The novelty with respect to previous likelihood reconstruction methods lies in the definition of a likelihood per single camera pixel, accounting not only for the total measured charge, but also for its development over time. This leads to more precise reconstruction of shower images. The method is applied to observations of the Crab Nebula acquired with the Large Size Telescope prototype (LST-1) deployed at the northern site of the Cherenkov Telescope Array.
The Cherenkov Telescope Array (CTA) is the next generation facility of Imaging Atmospheric Cherenkov Telescopes. It will reach unprecedented sensitivity and energy resolution in very-high-energy gamma-ray astronomy. CTA will detect Cherenkov light emitted within an atmospheric shower of particles initiated by cosmic-gamma rays or cosmic rays entering the Earth's atmosphere. From the combination of images the Cherenkov light produces in the telescopes, one is able to infer the primary particle energy and direction. A correct energy estimation can be thus performed only if the local atmosphere i…
Recent advances in unmanned aerial vehicle (UAV) technology have made UAVs an attractive possibility as an airborne calibration platform for astronomical facilities. This is especially true for arrays of telescopes spread over a large area such as the Cherenkov Telescope Array (CTA). In this paper, the feasibility of using UAVs to calibrate CTA is investigated. Assuming a UAV at 1 km altitude above CTA, operating on astronomically clear nights with stratified, low atmospheric dust content, appropriate thermal protection for the calibration light source and an onboard photodiode to monitor its …
The Cherenkov Telescope Array (CTA) will be the next generation gamma-ray observatory, which will consist of three kinds of telescopes of different sizes. Among those, the Large Size Telescope (LST) will be the most sensitive in the low energy range starting from 20 GeV. The prototype LST (LST-1) proposed for CTA was inaugurated in October 2018 in the northern hemisphere site, La Palma (Spain), and is currently in its commissioning phase. MAGIC is a system of two gamma-ray Cherenkov telescopes of the current generation, located approximately 100 m away from LST-1, that have been operating in s…
For reliable event reconstruction of Imaging Atmospheric Cherenkov Telescopes (IACTs), calibration of the optical throughput efficiency is required. Within current facilities, this is achieved through the use of ring shaped images generated by muons. Here, a complementary approach is explored, achieving cross calibration of elements of IACT arrays through pairwise comparisons between telescopes, focussing on its applicability to the upcoming Cherenkov Telescope Array (CTA). Intercalibration of telescopes of a particular type using eventwise comparisons of shower image amplitudes has previously…
The upcoming Cherenkov Telescope Array (CTA) project is expected to provide unprecedented sensitivity in the low-energy (<~100 GeV) range for Cherenkov telescopes. Most of the remaining background in this energy range results from misidentified hadron showers. In order to fully exploit the potential of the telescope systems it is worthwhile to look for ways to further improve the available analysis methods for γ/hadron separation. We study the composition of the background for the planned CTA-North array by identifying events composed mostly of a single electromagnetic subcascade or double sub…
Atmospheric parameters, such as pressure (P), temperature (T) and density, affect the development of extensive air showers initiated by energetic cosmic rays. We have studied the impact of atmospheric variations on extensive air showers by means of the surface detector of the Pierre Auger Observatory. The rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find that the observed behaviour is explained by a model including the effects associated with the variations of pressure and density. The former affects the longitudinal development of air showers while the latter influe…
The paper describes the techniques and method of registration of air shower radio emission at the Yakutsk array of extensive air showers at a frequency of 32 MHz. At this stage, emission registration involves two set of antennas, the distance between them is 500m. One set involves 8 antennas, second - 4 antennas. The antennas are perpendicularly crossed dipoles with radiation pattern North South,West East and raised 1.5 m above the ground. Each set of antennas connected to an industrial PC. The registration requires one of two triggers. First trigger are generated by scintillation detectors of…
Cosmic rays have valuable information about universe surroundings us. Finding energy, mass and arrival direction of primary cosmic ray particle are the most important aspects of extensive air shower studies. In order to determine these parameters, arrival direction and core position of extensive air showers should be determined at first. In this article, a new method has been introduced that utilizes arrival time information of secondary particles of extensive air showers for finding their core location and correcting plane wave front approximation so that calculate the arrival direction of ex…
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 t…
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 …
The Cherenkov Telescope Array (CTA), conceived as an array of tens of imaging atmospheric Cherenkov telescopes (IACTs), is an international project for a next-generation ground-based gamma-ray observatory, aiming to improve on the sensitivity of current-generation instruments a factor of five to ten and provide energy coverage from 20 GeV to more than 300 TeV. Arrays of IACTs probe the very-high-energy gamma-ray sky. Their working principle consists of the simultaneous observation of air showers initiated by the interaction of very-high-energy gamma rays and cosmic rays with the atmosphere. Ch…
The paper present correlation of radio signal with air shower parameters: shower energy E0 and depth of maximum Xmax. It is shown that from radio emission measurements of air showers one can obtain individual showers parameters and mass composition of cosmic rays. We also derived generalized formula for calculating energy of the air showers.
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.
AERA, the Auger Engineering Radio Array, located at the Pierre Auger Observatory in Malargüe, Argentina measures the radio emission of extensive air showers in the 30-80 MHz frequency range and is optimized for the detection of air showers up to 60$^{\circ}$ zenith angle. In this contribution the motivation, the status, and first results of the analysis of horizontal air showers with AERA will be presented.
We introduce a new Monte Carlo template-based reconstruction method for air shower arrays, with a focus on shower core and energy reconstruction of $γ$-ray induced air showers. The algorithm fits an observed lateral amplitude distribution of an extensive air shower against an expected probability distribution using a likelihood approach. A full Monte Carlo air shower simulation in combination with the detector simulation is used to generate the expected probability distributions. The goodness of fit can be used to discriminate between $γ$-ray and hadron induced air showers. As an example, we a…
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 paramet…
So far, cosmic ray air showers have been detected using scintillation counter arrays on the ground widely. And also air Cherenkov detection method, which is limited its observation period in moonless nights, has been adopted. The detection method of radio emission from cosmic ray air showers is not new, but rather old method. Radio emission from cosmic ray air showers has not been detected with the method of self-trigger system. If the detection method of radio emission were available, there is no limit of the observation like Cherenkov counter. The developments of high radio frequency (RF) te…
The Cherenkov Telescope Array (CTA) will be the world's largest and most sensitive ground-based gamma-ray observatory in the energy range from a few tens of GeV to tens of TeV. The LST-1 prototype, currently in its commissioning phase, is the first of the four largest CTA telescopes, that will be built in the northern site of CTA in La Palma, Canary Islands, Spain. In this contribution, we present a full-image reconstruction method using a modified InceptionV3 deep convolutional neural network applied on non-parametrized shower images. We evaluate the performance of optimized networks on Monte…
The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is a ground-based air shower array designed to detect Cherenkov light produced in water by secondary particles from atmospheric air showers. In order to improve the sensitivity at the highest energies, especially for the shower cores falling outside the main array, 345 smaller Water Cherenkov Detectors (WCDs) were installed around the main array, the outrigger array. This extension increased the instrumented area of HAWC by a factor of four. With the increased size of the array, and the ability to detect shower particles further aw…
High-energy cosmic rays impinging onto the atmosphere of the Earth initiate extensive air showers. With the LOFAR radio telescope and the Auger Engineering Radio Array (AERA) at the Pierre Auger Observatory radio emission from air showers is detected. Recent results are presented from both experiments. The measured properties of the radio emission are described. The measurements are used to derive the properties of high-energy cosmic rays: their arrival direction, energy, and particle type (mass).
The Auger Engineering Radio Array (AERA), at the Pierre Auger Observatory in Argentina, measures the radio emission of extensive air showers in the 30-80 MHz frequency range. AERA consists of more than 150 antenna stations distributed over 17 km$^2$. Together with the Auger surface detector, the fluorescence detector and the under-ground muon detector (AMIGA), AERA is able to measure cosmic rays with energies above 10$^{17}$ eV in a hybrid detection mode. AERA is optimized for the detection of air showers up to 60$^{\circ}$ zenith angle, however, using the reconstruction of horizontal air show…
Reflection of radio waves off the short-lived plasma produced by the high-energy shower particles in the air is simulated, considering various radar setups and shower geometries. We show that the plasma produced by air showers has to be treated always as underdense. Therefore, we use the Thomson cross-section for scattering of radio waves corrected for molecular quenching and we sum coherently contributions of the reflected radio wave over the volume of the plasma disk to obtain the time evolution of the signal arriving at the receiver antenna. The received power and the spectral power density…
In this paper we explore the possibility to complement the cosmic ray physics program of the IceCube observatory with an extended surface array of radio antennas. The combination of air-shower sampling on the surface and muon calorimetry underground offers significant scientifc potential: the neutrino sensitivity above the horizon can be enhanced by vetoing air-showers on the ground, photon-induced air-showers can be identifed by their small muon component and the coincident measurement of the particle density on the surface and the muon component gives useful information on the composition of…
We describe a method for restoring information lost during statistical thinning in extensive air shower simulations. By converting weighted particles from thinned simulations to swarms of particles with similar characteristics, we obtain a result that is essentially identical to the thinned shower, and which is very similar to non-thinned simulations of showers. We call this method dethinning. Using non-thinned showers on a large scale is impossible because of unrealistic CPU time requirements, but with thinned showers that have been dethinned, it is possible to carry out large-scale simulatio…
Imaging the radio-wave emission from extensive air showers
Radboud University Nijmegen（奈梅亨拉德堡德大学）；Nationaal Instituut voor Kernfysica en Hoge Energie Fysica (NIKHEF)（荷兰核与高能物理国家研究所）；Max-Planck-Institute for Nuclear Physics（马克斯·普朗克核物理研究所）
We present LOFAR measurements of radio emission from extensive air showers. We find that this emission is strongly polarized, with a median degree of polarization of nearly $99\%$, and that the angle between the polarization direction of the electric field and the Lorentz force acting on the particles, depends on the observer location in the shower plane. This can be understood as a superposition of the radially polarized charge-excess emission mechanism, first proposed by Askaryan and the geomagnetic emission mechanism proposed by Kahn and Lerche. We calculate the relative strengths of both c…
The radio intensity and polarization footprint of a cosmic-ray induced extensive air shower is determined by the time-dependent structure of the current distribution residing in the plasma cloud at the shower front. In turn, the time dependence of the integrated charge-current distribution in the plasma cloud, the longitudinal shower structure, is determined by interesting physics which one would like to extract such as the location and multiplicity of the primary cosmic-ray collision or the values of electric fields in the atmosphere during thunderstorms. To extract the structure of a shower …
Long-term series of measurement of spectral transparency of the atmosphere (λ= 430 nm) and atmospheric optical thickness (AOT) measured by multimode photometer CE 318 in the region of Yakutsk array are analyzed. Correlation of AOT with intensity of air showers with small energies 10^{15} - 10^{16} eV is found. The variability of aerosol composition of the atmosphere during the registration period of the Cherenkov light should be taken into account since it may affect the quality of determining characteristics of air showers.
The paper presents short technical description of Yakutsk Radio Array and some preliminary results obtained from measurements of radio emission at 32 MHz frequency induced by air shower particles with energy ε$\geq$1$\cdot$10$^{19}$ eV. The data obtained at Yakutsk array in 1987-1989 (first set of measurements) and 2009-2014 (new set of measurements). For the first time, at Yakutsk array radio emission from air shower with energy > 10$^{19}$ eV was registered including the shower with highest energy ever registered at Yakutsk array with energy $\sim$2$\cdot$10$^{20}$ eV.
The Cherenkov light produced in air showers largely contributes to the signal observed in ground-based gamma-ray and cosmic-ray observatories. Yet, no description of this phenomenon is available covering both regions of small and large angles to the shower axis. To fill this gap, a parametrization of the angular distribution of Cherenkov photons is performed in terms of a physically-motivated parametric function. Model parameters are constrained using simulated gamma-ray and proton showers with energies in the TeV to EeV region. As a result, a new parametrization is obtained that improves the …
Extensive air showers initiate the fluorescence emissions from nitrogen molecules in air. The UV-light is emitted isotropically and can be used for observing the longitudinal development of extensive air showers in the atmosphere over tenth of kilometers. This measurement technique is well-established since it is exploited for many decades by several cosmic ray experiments. However, a fundamental aspect of the air shower analyses is the description of the fluorescence emission in dependence on varying atmospheric conditions. Different fluorescence yields affect directly the energy scaling of a…
We consider the guaranteed physics of horizontal (hadron) air-showers, HAS, developing at high (tens km) altitudes. Their morphology and information traces are different from vertical ones. Hundreds of km long HAS are often split by geomagnetic fields in a long (fan-like) showering with a twin spiral tail. The horizontal fan-like airshowers are really tangent and horizontal only at North and South poles. At different latitude these showering plane are turned and inclined by geomagnetic fields. In particular at magnetic equator such tangent horizontal East-West airshowers are bent and developed…
A simple method for the parallelization of extensive air shower simulations is described. A shower is simulated at fixed steps in altitude. At each step, daughter particles below a specified energy threshold are siphoned off and tabulated for further simulation. Once the entire shower has been tabulated, the resulting list of particles is concatenated and divided into separate list files where each possesses a similar projected computation time. These lists are then placed on a computation cluster where the simulation can be completed in a piecemeal fashion as computing resources become availa…
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 …
The detection of air-shower events via radio signals requires to develop a trigger algorithm for a clean discrimination between signal and background events in order to reduce the data stream coming from false triggers. In this contribution we will describe an approach to trigger air-shower events on a single-antenna level as well as performing an online reconstruction of the shower parameters using neural networks.
The measurement of the radio emission from extensive air showers, induced by high-energy cosmic rays is one of the key science projects of the LOFAR radio telescope. The LOfar Radboud air shower Array (LORA) has been installed in the core of LOFAR in the Netherlands. The main purpose of LORA is to measure the properties of air showers and to trigger the read-out of the LOFAR radio antennas to register extensive air showers. The experimental set-up of the array of scintillation detectors and its performance are described.
