Extensive Air Shower Array Research Articles

Variable composition of cosmic rays with E 0 ≥ 1017 eV according to the data from the muon detectors of the Yakutsk EAS array

The lateral distribution of muons with the threshold E μ ≈ 1.0 secθ GeV (where θ is the zenith angle) in extensive air showers (EASs) with the energy E 0 ≈ 1017–19 eV in various observation periods from November 1987 to June 2013 has been analyzed. The experimental data have been compared to the calculations within various models of the development of EASs from the CORSIKA package. The experimental data are in the best agreement with the QGSJET II-04 model. The mass composition of cosmic rays with E 0 < 2 × 1018 eV before 1996 was much lighter than that in a later time interval.

Latest results on cosmic ray physics from the ARGO-YBJ experiment

Cosmic ray physics in the 1012–1015eV primary energy range is among the main scientific goals of the ARGO-YBJ experiment. The detector, located in the Cosmic Ray Observatory of Yangbajing (Tibet, China) at 4300m a.s.l., is a full coverage extensive air shower array consisting of a carpet of Resistive Plate Chambers (RPCs) distributed over an area of more than 10000m2. The apparatus layout, performance and location offer a unique opportunity for a detailed study of several characteristics of the hadronic component of the cosmic ray flux in an energy window marked by the transition from direct to indirect measurements. Moreover, the analog readout of the RPC signals indeed provides a powerful tool to study, with unprecedented resolution and without saturation, the extensive air shower space–time structure down to few meters from its axis. Latest results concerning the study of cosmic ray energy spectrum, mass composition and arrival directions will be given together with the search for an antiproton signal, the proton–air cross-section measurement, the study of the interplanetary magnetic field, and the effects of the geomagnetic field on secondary particles. Furthermore, particle distributions close to the shower axis are being extensively studied, also giving new inputs, in the very forward region, to the hadronic interaction models currently used for understanding particle physics and cosmic rays up to the highest energies.

TeV GAMMA-RAY SURVEY OF THE NORTHERN SKY USING THE ARGO-YBJ DETECTOR

The ARGO-YBJ detector is an extensive air shower array that has been used to monitor the northern $\gamma$-ray sky at energies above 0.3 TeV from 2007 November to 2013 January. In this paper, we present the results of a sky survey in the declination band from $-10^{\circ}$ to $70^{\circ}$, using data recorded over the past five years. With an integrated sensitivity ranging from 0.24 to $\sim$1 Crab units depending on the declination, six sources have been detected with a statistical significance greater than 5 standard deviations. Several excesses are also reported as potential $\gamma$-ray emitters. The features of each source are presented and discussed. Additionally, $95\%$ confidence level upper limits of the flux from the investigated sky region are shown. Specific upper limits for 663 GeV $\gamma$-ray AGNs inside the ARGO-YBJ field of view are reported. The effect of the absorption of $\gamma$-rays due to the interaction with extragalactic background light is estimated.

Medium scale anisotropy in the TeV cosmic ray flux observed by ARGO-YBJ

Measuring the anisotropy of the arrival direction distribution of cosmic rays provides important information on the propagation mechanisms and the identification of their sources. In fact, the flux of cosmic rays is thought to be dependent on the arrival direction only due to the presence of nearby cosmic ray sources or particular magnetic-field structures. Recently, the observation of unexpected excesses at TeV energy down to an angular scale as narrow as ∼10° raised the possibility that the problem of the origin of Galactic cosmic rays may be addressed by studying the anisotropy. The ARGO-YBJ experiment is a full-coverage extensive air showers array, sensitive to cosmic rays with the energy threshold of a few hundred GeV. Searching for small-size deviations from the isotropy, the ARGO-YBJ Collaboration explored the declination region δ∼−20°–80°, making use of about 3.7×1011 events collected from November 2007 to May 2012. In this paper, the detection of different significant (up to 13 standard deviations) medium-scale anisotropy regions in the arrival directions of cosmic rays is reported. The observation was performed with unprecedented detail. The relative excess intensity with respect to the isotropic flux extends up to 10−3. The maximum excess occurs for proton energies of 10–20 TeV, suggesting the presence of unknown features of the magnetic fields the charged cosmic rays propagate through, or some contribution of nearby sources never considered so far. The observation of new weaker few-degree excesses throughout the sky region 195°≤R.A.≤290° is reported for the first time.1 MoreReceived 29 April 2013DOI:https://doi.org/10.1103/PhysRevD.88.082001© 2013 American Physical Society

Scientific verification of High Altitude Water Cherenkov observatory

The High Altitude Water Cherenkov (HAWC) observatory is a TeV gamma-ray and cosmic-ray detector currently under construction at an altitude of 4100m close to volcano Sierra Negra in the state of Puebla, Mexico. The HAWC [1] observatory is an extensive air-shower array composed of 300 optically isolated water Cherenkov detectors (WCDs). Each WCD contains ~200,000l of filtered water and four upward-facing photomultiplier tubes. In Fall 2014, when the HAWC observatory will reach an area of 22,000m2, the sensitivity will be 15 times higher than its predecessor Milagro [2]. Since September 2012, more than 30 WCDs have been instrumented and taking data. This first commissioning phase has been crucial for the verification of the data acquisition and event reconstruction algorithms. Moreover, with the increasing number of instrumented WCDs, it is important to verify the data taken with different configuration geometries. In this work we present a comparison between Monte Carlo simulation and data recorded by the experiment during 24h of live time between 14 and 15 April of 2013 when 29 WCDs were active.

TeV ASTROPHYSICS WITH THE MILAGRO AND HAWC OBSERVATORIES

Ground-based gamma-ray astronomy has historically implemented two dramatically different techniques. One method employs Imaging Atmospheric Cherenkov Telescope(s) (IACT) that detect the Cherenkov light generated in the atmosphere by extensive air showers. The other method employs particle detectors that directly detect the particles that reach ground level — known as Extensive Air Shower (EAS) arrays. Until recently, the IACT method had been the only technique to yield solid detections of TeV gamma-ray sources. Utilizing water Chernkov technology, Milagro, was the first EAS array to discover new gamma-ray sources and demonstrated the power of and need for an all-sky high duty cycle instrument in the TeV energy regime. The transient nature of many TeV sources, the enormous number of potential sources, and the existence of TeV sources that encompass large angular areas all point to the need for an all-sky, high duty-factor instrument with even greater sensitivity than Milagro. The High Altitude Water Cherenkov (HAWC) Observatory will be over an order of magnitude more sensitive than Milagro. In this paper we will discuss the results from Milagro and the design of the HAWC instrument and its experimental sensitivity.

SN 1987A as a possible source of cosmic rays up to energy 1018 eV by Yakutsk EAS array data

Yakutsk extensive air shower array experiment is the only one which is in operation since 1974, it has the best exposure around 1018eV. It is believed that the balk of cosmic rays up to ~1017eV originated in supernova remnants [1]. Under certain conditions they can accelerate cosmic rays up to ~1018eV or even higher [2]. However, there is a lack of an undoubted observational evidence for such idea. Here we show that Yakutsk experiment probably has observed cosmic rays from SN 1987A. We found that before 1996 the intensity of cosmic rays in energy range 1017–1018eV fluctuate near some average value, then it start to increase. The increase of intensity total 45±5%. It is also accompanied by significant changes in cosmic ray composition; it became heavier – iron dominated. In the last 3-4 years it is a trend to return to the initial state. This peculiarities can be explained by the appearance of SN 1987A. If so, then our results demonstrate that supernova remnants can indeed accelerate cosmic rays up to ~1018e V. This is an important step in understanding the cosmic ray origin problem and reveal the great importance of long-term and multicomponent observations of ultra-high energy cosmic rays.

A METHOD TO SEARCH FOR CORRELATIONS OF ULTRA-HIGH ENERGY COSMIC-RAY MASSES WITH THE LARGE-SCALE STRUCTURES IN THE LOCAL GALAXY DENSITY FIELD

One of the main goals of investigations using present and future giant extensive air shower (EAS) arrays is the mass composition of ultra-high energy cosmic rays (UHECRs). A new approach to the problem is presented, combining analysis of arrival directions with the statistical test of the paired EAS samples. An idea of the method is to search for possible correlations of UHECR masses with their separate sources, for instance, if there are two sources in different areas of the celestial sphere injecting different nuclei, but fluxes are comparable so that arrival directions are isotropic, the aim is to reveal a difference in the mass composition of CR fluxes. The method is based on a non-parametric statistical test -- the Wilcoxon signed-rank routine -- which does not depend on the populations fitting any parameterized distributions. Two particular algorithms are proposed: first, using measurements of the depth of EAS maximum position in the atmosphere; and second, relying on the age variance of air showers initiated by different primary particles. The formulated method is applied to the Yakutsk array data, in order to demonstrate the possibility of searching for a difference in average mass composition of the two UHECR sets, arriving particularly from the supergalactic plane and a complementary region.

A method to search for correlations of UHECR masses with the large scale structures in the local galaxy density field

One of the main goals of investigations using present and future giant extensive air shower (EAS) arrays is the mass composition of ultra-high energy cosmic rays (UHECRs). A new approach to the problem is presented, combining analysis of arrival directions with the statistical test of the pairs of EAS samples. An idea of the method is to search for possible correlations of UHECR masses with their presumably separate sources. The method is based on a non-parametric statistical test, specifically Wilcoxon rank sum routine, which does not depend on the populations fitting any parameterized distributions.

Recent results from the GRAPES-3 experiment

The GRAPES-3 is a dense extensive air shower array operating with ~400 scintillator detectors and a 560 m2 large tracking muon detector (Eμ > 1 GeV), at Ooty in India. The muon detector has been used to observe acceleration of muons during thunderstorm conditions. The muon multiplicity distribution of the EAS is used to probe the composition of primary cosmic rays below 1 PeV, with an overlap with direct measurements. More recently we have explored the possibility of using the angular distribution of >1 GeV muons to identify the best from among several low- and high-energy hadronic interaction models. We have major expansion plans to enhance the sensitivity of the GRAPES-3 experiment in all of the areas listed above.

Recent results from the GRAPES-3 experiment

The GRAPES-3 is a dense extensive air shower array operating with ~400 scintillator detectors and a 560 m 2 large tracking muon detector (E μ > 1 GeV), at Ooty in India. The muon detector has been used to observe acceleration of muons during thunderstorm conditions. The muon multiplicity distribution of the EAS is used to probe the composition of primary cosmic rays below 1 PeV, with an overlap with direct measurements. More recently we have explored the possibility of using the angular distribution of >1 GeV muons to identify the best from among several low- and high-energy hadronic interaction models. We have major expansion plans to enhance the sensitivity of the GRAPES-3 experiment in all of the areas listed above.

Testing calculation results of Cherenkov radiation flux from extensive air showers using CORSIKA

This paper presents computational results of the spatiotemporal characteristics of Cherenkov light from particles of extensive air showers (EASs) induced by ultra-high-energy cosmic rays (UHECR). These results were obtained by simulating EAS events with the CORSIKA software package. Events were induced by UHECR particles, i.e., protons and iron nuclei with energies of 1015 and 1016 eV. The computational results were compared with experimental data obtained at the Yakutsk EAS array; possible causes of the discrepancy between them are discussed.

Composition of cosmic rays at ultra high energies

We present measurements of the cosmic ray (CR) composition above 1015eV, performed with the Yakutsk extensive air shower array. Almost 42,000 events above 1017eV observed by Cherenkov detectors are selected for the analysis of the depth of maximum of the longitudinal development of air showers induced by CRs. The interpretation of these results in terms of CR mass composition is given. It is shown that mean logarithm of the CR atomic number 〈lnA(ϵ)〉 is characterized by the peak value 〈lnA〉≈2.5 achieved at ϵ∼1017eV and its substantial decrease within the energy interval 1017−1018eV to 〈lnA〉≈1 at ϵ>1018eV. Such a behavior can be considered as indication for the transition from galactic CR component, which is produced in galactic supernova remnants, to extragalactic CR component at ϵ=1017−1018eV.

Hadrons with energies of &lt;i&gt;E&lt;sub&gt;h&lt;/sub&gt;&lt;/i&gt; &gt; 50 MeV in EAS with &lt;i&gt;N&lt;sub&gt;e&lt;/sub&gt;&lt;/i&gt; = 10&lt;sup&gt;5&lt;/sup&gt;&amp;ndash;10&lt;sup&gt;7&lt;/sup&gt;

The characteristics of hadrons with Eh > 50 MeV in EAS have been obtained. The measurements were per- formed at the CARPET-2 extensive air shower array. For showers with E0 > 6· 10 13 eV the duration of hadronic cas- cade in NM has been estimated. The dependence of the mean neutron multiplicity in the neutron monitor on the total num- ber of the change particles for EAS with Ne = 10 5 10 7 at a distance of 17 30 m from EAS axis has been measured. it is equipped with registration system which enables time in- tervals between pulses to be recorded with accuracy 1 µs. It allows studying such phenomenon as a neutron multiplicity, induced by hadrons of EAS.

THE ARGO-YBJ EXPERIMENT: A FULL COVERAGE ARRAY FOR γ-RAY ASTRONOMY

The ARGO-YBJ experiment is an Extensive Air Shower (EAS) array which combines high altitude location and full coverage active area in order to reach low energy threshold at a level of few hundred of GeV. The large field of view (≈ 2 sr ) and the high duty cycle (≥ 90%) allow the continuous monitoring of the sky searching for unknown sources and unpredictable events, such as flares in blazar emissions and high energy Gamma-Ray Bursts (GRBs). In this paper I will briefly report on the detector performance and on some preliminary results achieved in γ-ray astronomy.

Developments in shower reconstruction and composition analysis for CARPET-3 EAS array

This contribution describes the current progress on the composition analysis of data recorded with Carpet EAS detector. The focus of the paper is on the methodologi- cal side of analysis. A study of the primary composition in the PeV region can currently be carried out solely by means of extensive air shower (EAS) measurements. These measurements rely on the use of different particle interaction models describing the development of EAS in the atmosphere and indicate that the mass composition of primary spectrum change in the PeV re- gion, as reviewed and discussed by Blet al. (2009). As direct experiments measuring the primary particle spectrum at and above the PeV region are not in the foreseeable future, further ground based observations on the properties of EAS with different detection and analysis techniques are needed. Precision measurements of the lateral density functions (LDFs) of charged particles in EAS have been performed with the Carpet EAS array. This measurement can give fur- ther light on the composition of the primary cosmic-ray par- ticles in the knee region. This contribution focuses on some of the aspects relevant to the development of the new methods of analysis of the Carpet EAS data. The experimental LDFs, compared with simulated ones (CORSIKA QGSJET 01C,Heck et al., 1998), are presented and further description is given on the progress of the development of analysis methods. Such developments are needed for analysis of new data and for analysis of the newly proposed Carpet-3 EAS array.

Gamma Rays observation with EAS detectors

Large extensive air shower (EAS) arrays provide complementary technology for observation of very high-energy gamma rays. Whereas their instantaneous sensitivity is currently a factor ∼ 150 less than that of imaging atmospheric Cherenkov telescopes (IACTs), their large field of view (∼ 90 deg; 1.8 sr) and nearly 100% duty cycle makes these observatories particularly suited to conduct all-sky surveys and to detect emission from extended astrophysical sources. Due to the wide field of view coverage of the sky and uninterrupted operation, the EAS technique has also the potential to detect of very high energy (VHE) transient phenomena.

Constraints on the flux of primary cosmic-ray photons at energiesE&gt;1018 eVfrom Yakutsk muon data

Comparing the signals measured by the surface and underground scintillator detectors of the Yakutsk Extensive Air Shower Array, we place upper limits on the integral flux and the fraction of primary cosmic-ray photons with energies E > 10^18 eV, E > 2*10^18 eV and E > 4*10^18 eV. The large collected statistics of the showers measured by large-area muon detectors provides a sensitivity to photon fractions < 10^-2, thus achieving precision previously unreachable at ultra-high energies.

Main results of the study of ultrahigh-energy cosmic rays in the Yakutsk Extensive Air Shower Array

This paper describes the current state of the Yakutsk Extensive Air Shower Array (EASA) and the prospects for its modernization. The main results of the study of the energy spectrum, mass composition, and anisotropy of the ultra-high energy cosmic rays (UHECRs) that were obtained recently by the array are given.

Cosmic ray physics with the ARGO-YBJ experiment

Cosmic ray physics in the 10 12–10 15 eV primary energy range is among the main scientific goals of the ARGO-YBJ experiment. The detector, located at the Cosmic Ray Observatory of Yangbajing (Tibet, P.R. China) at 4300 m a.s.l., is a full coverage Extensive Air Shower array consisting of a carpet of Resistive Plate Chambers of about 6000 m 2. The apparatus layout, performance and location offer a unique possibility to make a deep study of several characteristics of the hadronic component of the cosmic ray flux in an energy window marked by the transition from direct to indirect measurements. In this work we will focus on the experimental results concerning the measurements of the primary cosmic ray energy spectrum and of the proton-air cross-section. The all-particle spectrum has been measured, by using a bayesian unfolding technique, in the 1–100 TeV energy region. The proton-air cross-section has been measured at the same energies, by exploiting the cosmic ray flux attenuation for different atmospheric depths (i.e. zenith angles). The total proton–proton cross-section has then been estimated at center of mass energies between 70 and 500 GeV, where no accelerator data are currently available.