Small Showers Research Articles

Intermittent behaviour in small CORSIKA showers

In this work we are concerned with the quantitative study of correlations between charged particles: electrons/positrons and muons in small Extensive Air Showers. By “small”, we mean showers that are initiated by primary protons with energies of up to ∼1 TeV. We study the strength of these correlations with the help of the CORSIKA simulation program. The results show the ‘intermittent’ behaviour of the density distributions. This is particularly evident for the electron component of very small showers with primary particle energies on the order of 100 GeV or less, where the shower consists of up to ten or so charged particles. For shower muons, the correlations are significantly smaller, and it is important to determine the values of the residual correlations for experiments that are shielded from the electron component. Detectors in surface shower arrays that measure both hard and soft component particles are by design sensitive to a superposition of strong electron correlations and weak or even non-existent correlations in the muon component. This folding is not trivial, and we show how it ends up getting folded. This is interesting in itself, and the specific values of the scaled factor moments allow us to estimate the possible effects of these large non-Poisson fluctuations. This may be relevant to the analysis of data from small shower arrays and other atypical experimental facilities where cosmic ray particles are an unwanted background.

Testing the superposition model in small CORSIKA shower simulations

The idea of superposition in the high-energy interactions of cosmic ray nuclei and the development of extensive air showers initiated by them has been known for more than half a century. It has been thoroughly and successfully tested in a number of simulations for primary energies around 1015 and above. In this work, we will investigate its applicability to lower energies. At the lowest energies, when the shower contains on average about one charged particle (or even less), deviations from the superposition model can be seen in the simulation results. Fluctuations of higher moments of the main shower parameters are systematically broader than expected. Further studies to confirm superposition in particular in the shower longitudinal profile are in progress. A correct description of the longitudinal development of the small shower, a precise description of its fluctuations on the observational level with a correct implementation of the superposition principle will enable to construct a simple and fast phenomenological algorithm generating small showers indispensable for the interpretation of measurements made using a small local shower array and determination of the flux of single, incoherent, secondary cosmic ray particles.

Characteristics of extensive air showers around the energy threshold for ground-particle-based gamma -ray observatories

Very-high-energy gamma -ray astronomy based on the measurement of air shower particles at ground-level has only recently been established as a viable approach, complementing the well established air Cherenkov technique. This approach requires high (mountain) altitudes and very high surface coverage particle detectors. While in general the properties of air showers are well established for many decades, the extreme situation of ground-level detection of very small showers from low energy primaries has not yet been well characterised for the purposes of gamma -ray astronomy. Here we attempt such a characterisation, with the aim of supporting the optimisation of next-generation gamma -ray observatories based on this technique. We address all of the key ground level observables and provide parameterisations for use in detector optimisation for shower energies around 1 TeV. We emphasise two primary aspects: the need for large area detectors to effectively measure low-energy showers, and the importance of muon identification for the purpose of background rejection.

Meteor Observations at Kazan Federal University (Russia)

SummaryThis poster paper described initial results of recent meteor observations in Kazan obtained with a new meteor radar, SKiYMET. Significant improvements in the number of registrations are being recorded, enabling better statistics.Radar observations of meteors have been carried out and archived since the mid-20th Century; at Kazan University (56°N, 49°E) they commenced in 1956, and have continued with only a few interruptions. A quasi-tomographic method (developed in-house in 2000) has been used to determine the coordinates of radiants of meteor showers, and to derive the orbital elements of small showers (microshowers).The observations provide valuable information about the distribution of meteoric matter near the Earth’s orbit. That information supports studies of stratospheric temperatures. A new radar, SKiYMET, was deployed in 2015 and measured parameters such as meteor speeds, but in 2016 its software was supplemented by an in-house package which performed more efficient pre-filtering of the primary data to eliminate non-meteor reflections from various sources. The new filtering algorithm has reduced substantially the threshold S/N ratio for detecting meteors (so fainter meteors can now be recorded), while the package also enables meteor velocities to be calculated much more efficiently than with SKiYMET, improving significantly the quality and statistical indicators of the processed data. By detecting a much larger number of meteors, it enables more detailed studies of the distribution of meteor velocities per day and per season.Daily meteor counts for 2016–2017, extracted from the observations by the KFU programme, yielded significantly higher rates than with SKiYMET. These results support much better statistics, and also enable much finer details to be discerned. In particular, plots of meteor rates against speed are found to exhibit two maxima, one near 30 km s−1 and one near 55 km s−1. This bifurcation in the relationship can also be discerned in the seasonal dependences of the speed distribution.Improvements in the measurements of the speeds of meteor particles entering the atmosphere reveal an increase in the numbers with higher speeds (> 50 km s−1). The distributions of speeds and heights show a rather strong dependence of the meteor speed upon altitude; as predicted by meteor physics, those with higher speeds begin to burn at higher altitudes. A local increase in the number of meteors that have speeds of about 55 km s−1 has also been reported in the literature. The increase could be associated with heterogeneities in the distribution of meteoric matter in the vicinity of the Earth’s orbit.

Sensitivity study of (10,100) GeV gamma-ray bursts with double shower front events from ARGO-YBJ**Supported by National Natural Science Foundation of China (11475141) and Fundamental Research Funds for Central Universities (2682014CX091)

ARGO-YBJ, located at the Yangbajing Cosmic Ray Observatory (4300 m a.s.l., Tibet, China), is a full coverage air shower array, with an energy threshold of ∼300 GeV for gamma-ray astronomy. Most of the recorded events are single front showers, satisfying the trigger requirement of at least 20 particles detected in a given time window. However, in ∼11.5% of the events, two randomly arriving showers may be recorded in the same time window, and the second one, generally smaller, does not need to satisfy the trigger condition. These events are called double shower front events. By using these small showers, well under the trigger threshold, the detector primary energy threshold can be lowered to a few tens of GeV. In this paper, the angular resolution that can be achieved with these events is evaluated by a full Monte Carlo simulation. The ARGO-YBJ sensitivity in detecting gamma-ray bursts (GRBs) by using double shower front events is also studied for various cutoff energies, time durations, and zenith angles of GRBs in ARGO’s field of view.

An EAS event observed in the early stage of development

Since 1969 the experiments of Brazil-Japan Collaboration showed the occurrence of a series of events, showing a region with a high concentration of electromagnetic particles, surrounded by isolated and/or groups of showers. These events were named “halo events” or “super-families”. Currently, we have more than a dozen of such events. The first of them, due to its aspect, was named “Andromeda”. We present here the main characteristics of a similar halo event, named C21S087I075. It has a halo region with many high energy showers in its border. Other small energy showers spread over the central and surrounding blocks (S088, S100, S101, I074). These isolated showers, classified as of hadronic or electromagnetic origin, present a fractional energy distribution compatible with that of a Centauro candidate event (C16S087I037), reported at this symposium [S.L.C. Barroso, P.C. Beggio, J.A. Chinellato, A.O. Carvalho, A. Mariano, R. Oliveira, E.H. Shibuya, in this issue of XIV ISVHECRI]. Moreover, the lateral distribution in the halo region is similar to that observed in other 3 halo events.

Microshower Structure of the Meteor Complex

Meteor radar observations of ionized trails in the Earth’s atmosphere provide observations that do not depend on weather conditions and time of day and provide good statistics for analysis. Further development in the new quasitomographic analysis of the goniometric data of the Kazan meteoric radar has revealed a number of very weak meteoric streams with rates of more than 5–6 meteors per day. In addition to the known large meteor showers, we have found up to as many as 1000 small showers per month that we have named microshowers. We shall operationally define a microshower as the minimal meteoric stream which can be detected with the Kazan meteoric radar while quasitomographic procedures of processing interferometer data are used.

Observation of GeV Solar Energetic Particles from the 1997 November 6 Event Using Milagrito

Milagrito was an extensive air-shower observatory that served as a prototype for the larger Milagro instrument. Milagrito operated from 1997 February to 1998 May. Although it was designed as a very high energy (few hundred GeV threshold) water-Cerenkov gamma-ray observatory, it could also be used to study solar energetic particles (SEPs). By recording scaler data, which correspond to photomultiplier tube singles rates, it was sensitive to muons and small showers from hadronic primary particles with rigidities above ~4 GV. Milagrito simultaneously recorded air-shower trigger data of primary particles with energies greater than ~100 GeV that provide the data to help reconstruct event directions. The Milagrito scalers registered a ground-level enhancement associated with the 1997 November 6 SEP event and X9 solar flare. At its peak, the enhancement was 22 times the background rms fluctuations. Based on comparisons to neutron monitor and satellite data, we find evidence that the rigidity power-law spectrum for the differential flux of energetic protons steepened above ~4 GV and that the acceleration site was high in the corona (at ~3 R☉ above the photosphere), assuming that a CME-driven shock was responsible for the ground-level enhancement.

Strategies for selection of small γ-ray showers using the Imaging Atmospheric Cherenkov Technique

Abstract Methods of selecting small candidate γ-ray events obtained using the Imaging Atmospheric Cherenkov Technique are presented. Three approaches are described: a variant of the standard ‘Supercuts’ analysis technique, a parameter weights approach, and a neural network approach. A cut on the parameter combination Length/Size is developed and shown to be effective at rejecting background due to muons. The techniques are applied to observations of Markarian 421 taken during 1995 and 1996 with the Whipple 10 m reflector. The efficiency and stability of the three approaches are compared, and the Supercuts variant is shown to be the most robust. A signal is detected in the energy range 170 GeV to 300 GeV at a significance level of 6.5 σ, in 7 hours of observation (the standard analysis gives 15.2 σ for E > 300 GeV). This represents the first significant detection of a source at an energy threshold below 200 GeV using the Whipple 10 m system.

A hypothesis to explain lichen-Rangifer dynamic relationships

A small group of fruticous lichen species, viz. Cetraria nivalis, Cladonia mitis, C. stellaris, and Stereocaulon paschale forms extensive mats in the most winter habitats of Rangifer tarandus populations in Norway. The plant communities accessible for grazing are often found on easily drained, moraine ridges. These lichen species are perennial, lying on the ground while growing slowly at the top. As they decompose they add humus to the top of the soil profile. The lichen mats catch all water from small showers, thus preventing vascular plants from obtaining a more regular water supply. Grazing removs whole plants and gradually makes larger and larger holes in the lichen mats. Wind and water erode the humus, with only coarse gravel remaining. This diminishes the soil water storage capacity. Without grazing, lichens will gradually build a humus layer, which would improve the soil water storage capacity. In time vascular plants then would take the place of the lichens. I propose the hypothesis that by (over-)grazing Rangifer improve their winter pastures by making conditions more favourable for lichens than for vascular plants.The fact that lichens are more scarce on habitats with more and regular precipitation, 1) in more oceanic climates, 2) on soils with more silt, and 3) on bird perches with thick peat due to regular fertilising, support this hypothesis.

A cosmic ray air shower array for the study of gamma ray transients

An air shower array consisting of eight plastic scintillation detectors has been constructed to search for bursts of high energy cosmic gamma rays over a wide variety of time scales. The design and performance of the array are described in detail. The array has a low energy threshold, good sensitivity to small showers and an angular accuracy of a few degrees in determining the shower arrival direction.

Splash dispersal inColletotrichum graminicola (Ces.) Wilson, the causal organism of anthracnose of sorghum

The conidia ofColletotrichum graminicola (Ces.) Wilson were dispersed only by rain drops. The dispersal was related to the frequency of rainfall. Under field conditions, conidia were dispersed vertically up to a height of 0·75 m and laterally up to a distance of 1 m from the source. Both incident water drops and flowing water liberated conidia from the sporulating lesions. Peak liberation of conidia occurred with the water drops 3–11, and most conidia were removed from the sporulating lesions within 60 s, suggesting dispersal of the pathogen even during small showers of rain.

New aspects of muon and electron abundance in small EAS

A three-dimensional simulation of muon and electron components has been performed for showers with energies 2*104 and 2*107 GeV, using a model which takes into account the most important results in recent UA1 and UA5 CERN collider data. Lateral muon structure functions become steeper with increasing energy and the index alpha in Delta mu approximately=Nealpha decreases with distance from values near 0.85 around 5 m down to 0.43 at approximately 2 km from the shower axis, at a fixed depth of 700 g cm-2 (this variation is even more important at sea level). Since densities in small showers are recorded inside 50 m, an apparent exponent alpha which is observed to be around 0.75 can ultimately be in agreement with alpha =0.68 in Nmu approximately=ealpha (and similarly at sea level); consequently heavy compositions or different multiproduction need no longer be invoked to explain this aspect of cosmic-ray data, at least in the energy band 2*104-2*105 GeV.

The Oklahoma Squall Line of 19 May 1977. Part II: Mechanisms for Maintenance of the Region of Strong Convection

Mechanisms for maintenance of the strong convection along the leading edge of a broad squall line that occurred in Oklahoma on 19 May 1977 are investigated. The findings are based upon analysis of data from a surveillance radar, a surface mesonetwork, Doppler radars, proximity soundings and aircraft data, and upon the results of a two-dimensional, cloud-scale numerical simulation. The detailed results of the multiple Doppler analysis are contained in the Part I paper reporting results of research on this squall line. It is found that at a preferred location along the squall line, an area of intense convection is maintained over a long time period. A meso-β scale organized structure, which includes an area of low pressure near the southeast edge of the intense convection and an associated area of convergence extending to the east, promotes the formation of small showers in short line segments. These showers, due to their differing motion from elements within the main line, merge with the line to the north of the mesolow, resulting in maintenance of the strong area of convection. The observed meso-β structure on this day is believed to be made possible by a deep low-level layer of weak vertical wind shear and high water-vapor content. At other locations along the line, the numerical simulation indicates an unsteady behavior in the maintenance of squall line convection by gust frontal convergence. Perturbations in the vertical motion field are periodically initiated by either (i) enhanced convergence at the gust front resulting from diverging downdrafts at locations farther to the west, or (ii) Kelvin-Helmholtz instability produced at the gust front head. These perturbations move westward relative to the gust front above the low-level cold air and periodically invigorate the main region of updrafts located a few tens of kilometers west of the gust front. Low-level updrafts, forced by diverging surface outflow from weak downdrafts, occasionally interact with the translating perturbations to increase their amplitude. The existence of the westward-moving perturbations is tentatively substantiated by the presence of similar structures in the analyzed Doppler wind fields. Greater time resolution in Doppler data, in combination with more comprehensive surface and upper air data ahead of squall lines of this type, would aid in confirming the reported structures.

The sensitivity of Cerenkov radiation pulses to the longitudinal development of cosmic-ray showers

Monte-Carlo simulation of electron-photon cascades in the atmosphere have been used to calculate fluxes and time distributions of Cerenkov radiation from air showers. Results are presented which allow the longitudinal development of cosmic-ray showers to be mapped from the time structure of Cerenkov pulses (assuming perfect instrumental time resolution) without further recourse to hadron interaction models. Mapping of the development becomes unreliable using pulses observed much within 170-200 m of the axis (depending on zenith angle). The use of angular distributions given in a preceding paper (ibid., vol.8, p.1461, 1982) proved to be a satisfactory substitute for detailed Monte-Carlo cascade simulations for calculating Cerenkov signals. A sharp shoulder is expected to develop in the lateral distribution of the light in small showers; this should be allowed for in analysing observations.

Monte Carlo simulation of small air-mass showers

The present model permits simulation of any geographic region and the symmetrical or random positioning of any number of rain gauges. The operator has the option of entering precipitation parameters: rain cell diameter, duration, rain swath length, vector angle, and precipitation amount for any number of discrete showers. In a series of computations the model generates (1) a random ‘first echo’ location and resulting rain swath, which is superimposed on a specific grid of rain gauges; (2) the number of rain gauge receiving a hit; and (3) the number of undetected rain events within an area.

An experiment to detect y-rays of energy above 1000 GeV from Cygnus X-3

High energy y-rays, of energies greater than 10 12 eV, have been detected from Cyg X-3 (Vladimirski et al. 1973; Mukanov et al. 1979). In both experiments, 1.5 m diameter flux collectors were used to detect optical Cherenkov radiation from the small electron showers in the atmosphere. The background radiation due to cosmic ray protons was rejected in both cases by performing drift scans across the position of the object.

A fast optical Cerenkov system for directional studies of possible gamma-ray sources

The system observes pulses of light from the night sky, produced by small showers in the atmosphere. It uses two 90-cm f/0.5 mirrors in coincidence and with effective full field of view about 1°; but unlike previous systems of this kind it has a reduced integration time of about 3 ns and coincidence resolving time of 5 ns, the object being the selection of the fast collimated light cone originating from the high-energy early generations of the shower above 10 km rather than the slower, less directed, but more intense component from the vicinity of the maximum. The threshold energy for γ-rays showers is difficult to determine from the observed counting rate for proton showers, since the early development of the showers is different, but is believed to be in the vicinity of 1012 eV. Preliminary drift scans have been carried out in the winter of 1966–67 at a site 300 m above sea level near Dublin. Several drift scans have been carried out on the Crab nebula, 3C196, and 3C286; and individual runs on some other objects including a possible source of neutral primaries at about 1100 + 20 reported by Hesse et al. The Crab nebula results show an apparent positive effect which, if it is real, would correspond to a flux of about 10−10 photons/cm2 s, but the results are difficult to assess because of poor atmospheric conditions. Some other apparent positive effects have been observed, but none are significant statistically.

Ultra-high-energy Nuclear Interactions and Extensive Air Showers

The `kink' in the size spectrum of extensive air showers occurs at a similar size at all altitudes, although shower absorption measurements indicate that there is an attenuation of particle numbers with depth. It follows that the cause cannot be the shape of the primary energy spectrum, but must lie in the properties of nuclear interactions. The author proposes a model in which the elasticity of nuclear interactions increases from about 0.5 to 0.7 as the interaction energy becomes greater than 5 × 1013 eV. The mean energy of the secondary pions is also supposed to increase. As a result, in small showers the individual electron photon cascades are short, and large fluctuations in development can occur, whereas for large showers the fluctuations are small. The model is shown to be consistent with most of the experimental evidence, including the size spectrum kink, a decrease in the degree of fluctuation in certain measurements as shower size increases, and a rapid change in the properties of the shower core.

On the $${\mathcal{N}}$$ -component in extensive air showers-component in extensive air showers

According toNikolskijet al. (1957), the number of nuclear-active (\({\mathcal{N}}\)) particles in air showers increases fairly slowly, asE0.2, for showers ranging in energy from 1013 eV to 1015 eV. At energies >1015 eV the increase is more rapid and is ∝E. This variation in the\({\mathcal{N}}\)-component with the size of the shower and certain other observed features of air showers have been interpreted previously as an indication of a change in the nature of nuclear interactions at very high energies or as an indication of specific details in the nature and composition of the primary cosmic radiation, such as the existence of a cut-off in the magnetic rigidity of the particles and the predominance of heavy primaries at very high energies. In this paper an attempt is made to explain the above observed features in terms of certain characteristics of nucleon-nucleus (\(n - {\mathcal{N}}\)) pion-nucleus (\(\pi - {\mathcal{N}}\)) collisions; the term « nucleus » here refers to an « air nucleus ». The main aspect of the (Nikolskij) curve, for the abundance of\({\mathcal{N}}\)-particlesvs. shower energy, considered here, is not the rapid increase of the\({\mathcal{N}}\)-component in showers of energy >1015 eV, nor the existence of a change in the abundance of\({\mathcal{N}}\)-particles in going from small showers to big showers, but rather the fairly slow increase in the number of\({\mathcal{N}}\)-particles in showers of energy (1013÷1015) eV. This slow increase, which is contrary to general experience in cascade calculations, puts stringent limitations on the choice of parameters that characterize\(n - {\mathcal{N}}\) and\(\pi - {\mathcal{N}}\) collisions. It is shown that\(n - {\mathcal{N}}\) and\(\pi - {\mathcal{N}}\) collisions are largely elastic and that the number of secondary nucleons produced in such collisions is quite small (of the order of one or two); further, in a\(\pi - {\mathcal{N}}\) collision, the energy going into the nucleon component is a very small fraction of the energy of the incident pion. These features also result in a rapid increase in the\({\mathcal{N}}\)-component of big showers; this arises as a result of the complicated role played by charged pions owing to their finite life time. In small showers the charged pions have only small energies and hence they mostly decay and do not contribute appreciably to the\({\mathcal{N}}\)-component. In big showers, however, the pions have sufficiently high energy to make nuclear interactions before decaying and owing to the large multiplicity of pions produced in\(n - {\mathcal{N}}\) and\(\pi - {\mathcal{N}}\) collisions, there is a rapid increase in the number of\({\mathcal{N}}\)-particles with increasing energy of the shower. Some experiments are suggested to distinguish between the various possible explanations.