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1.
Anisotropy in the arrival directions of cosmic rays with energies above 1017 eV is studied using data from the Akeno 20 km2 array and the Akeno Giant Air Shower Array (AGASA), using a total of about 114 000 showers observed over 11 years. In the first harmonic analysis, we have found a strong anisotropy of 4% around 1018 eV, corresponding to a chance probability of 0.2% after taking the number of independent trials into account. with two-dimensional analysis in right ascension and declination, this anisotropy is interpreted as an excess of showers near the directions of the Galactic Center and the Cygnus region.  相似文献   

2.
An interpretation of Akeno giant air shower array (AGASA) data by comparing the experimental results with the simulated ones by cosmic ray simulation for KASCADE (CORSIKA) has been made. General features of the electromagnetic component and low energy muons observed by AGASA can be well reproduced by CORSIKA. The form of the lateral distribution of charged particles agrees well with the experimental one between a few hundred metres and 2000 m from the core, irrespective of the hadronic interaction model studied and the primary composition (proton or iron). It does not depend on the primary energy between 1017.5 and 1020 eV as the experiment shows. If we evaluate the particle density measured by scintillators of 5 cm thickness at 600 m from the core S0(600), suffix 0 denotes the vertically incident shower) by taking into account the similar conditions as in the experiment, the conversion relation from S0(600) to the primary energy is expressed as E (eV)=2.15×1017S0(600)1.015 within 10% uncertainty among the models and composition used, which suggests the present AGASA conversion factor is the lower limit. Although the form of the muon lateral distribution fits well to the experiment within 1000 m from the core, the absolute values change with hadronic interaction model and primary composition. The slope of the ρμ(600) (muon density above 1 GeV at 600 m from the core) vs. S0(600) relation in experiment is flatter than that in simulation of any hadronic model and primary composition. As the experimental slope is constant from 1015 to 1019 eV, we need to study this relation in a wide primary energy range to infer the rate of change of chemical composition with energy.  相似文献   

3.
The arrival directions of cosmic rays with energies above 1019 eV using data from EAS world arrays are considered. The problem of searching for clusters in arrival directions of the extensive air shower arrays at Yakutsk, Haverah Park, Volcano Ranch, Sydney and Akeno are examined. Four cluster directions are identified which are believed to be significant: these clusters do not lie in the direction of the Galactic Plane.  相似文献   

4.
Linsley used the Volcano Ranch array to collect data on the lateral distribution of showers produced by cosmic rays at energies above 1017 eV. Very precise measurements of the steepness of the lateral distribution function were made on 366 events. The current availability of sophisticated hadronic interaction models has prompted an interpretation of the measurements. In this analysis we use the Monte Carlo code to generate showers, together with to simulate the detector response to ground particles. The results show that, with the assumption of a bi-modal proton and iron mix, iron is the dominant component of cosmic rays near 1018 eV, assuming that hadronic interactions are well-described by at this energy range. The Volcano Ranch data set, as available to us, does not allow a straightforward assignment of energy for each event. It is thus not possible to give the energy dependence of the mass composition.  相似文献   

5.
The energy spectrum of cosmic rays with primary energies between 1014 eV and 1016 eV has been studied with the CASA-MIA air shower array. The measured differential energy spectrum is a power law (dj/dE ∝ E−y) with spectral indices γ of 2.66±0.02 below approximately 1015 eV and 3.00±0.05 above. A new method is used for measuring primary energy derived from ground-based data in a compositionally insensitive way. In contrast with some previous reports, the “knee” of the energy spectrum does not appear sharp, but rather a smooth transition over energies from 1015 eV to 3.0 × 1015 eV.  相似文献   

6.
《Astroparticle Physics》2004,21(6):565-581
The mass composition of high-energy cosmic rays at energies above 1015 eV can provide crucial information for the understanding of their origin. Air showers were measured simultaneously with the SPASE-2 air shower array and the AMANDA-B10 Cherenkov telescope at the South Pole. This combination has the advantage to sample almost all high-energy shower muons and is thus a new approach to the determination of the cosmic ray composition. The change in the cosmic ray mass composition was measured versus existing data from direct measurements at low energies. Our data show an increase of the mean log atomic mass lnA by about 0.8 between 500 TeV and 5 PeV. This trend of an increasing mass through the “knee” region is robust against a variety of systematic effects.  相似文献   

7.
On the origin of highest energy cosmic rays   总被引：1，自引：0，他引：1  
In this paper we show that the conventional diffusive shock acceleration mechanism for cosmic rays associated with relativistic astrophysical shocks in active galactic nuclei (AGNs) has severe difficulties to explain the highest energy cosmic ray events. We show that protons above around 2 x 1020 eV could have marginally been produced by this mechanism in an AGN or a rich galaxy cluster not further away than around 100 Mpc. However, for the highest energy Fly's Eye and Yakutsk events this is inconsistent with the observed arrival directions. Galactic and intergalactic magnetic fields appear unable to alter the direction of such energetic particles by more than a few degrees. We also discuss some other options for these events associated with relativistic particles including pulsar acceleration of high Z nuclei. At the present stage of knowledge the concept of topological defects left over from the early universe as the source for such events appears to be a promising option. Such sources are discussed and possible tests of this hypothesis are proposed.  相似文献   

8.
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.  相似文献   

9.
《Astroparticle Physics》2005,22(5-6):339-353
Data taken during 1997 with the AMANDA-B10 detector are searched for a diffuse flux of neutrinos of all flavors with energies above 1016 eV. At these energies the Earth is opaque to neutrinos, and thus neutrino induced events are concentrated at the horizon. The background are large muon bundles from down-going atmospheric air shower events. No excess events above the background expectation are observed and a neutrino flux following E−2, with an equal mix of all flavors, is limited to E2Φ(1015 eV < E < 3 × 1018 eV)  0.99 × 10−6 GeV cm−2 s−1 sr−1 at 90% confidence level. This is the most restrictive experimental bound placed by any neutrino detector at these energies. Bounds to specific extraterrestrial neutrino flux predictions are also presented.  相似文献   

10.
O+(4S) + H2O charge-transfer cross-section and product-ion time-of-flight measurements are presented over a center-of-mass collision energy range of 0.2–15 eV. The results are obtained with a newly constructed guided-ion beam experiment. The measured energy dependence of the charge-transfer crosssection agrees well with previous measurements and ADO model predictions of Bates [Chem. Phys. Lett. 82, 396 (1981) Proc. R. Soc. Lond. A384, 289 (1982) Chem. Phys. Lett. 111, 428 (1984)] at low collision energies, but exhibits significant differences at collision energies above 2 eV. The product kinetic energy analysis shows that most of the product ions are produced with near-thermal kinetic energies. At low collision energies, a significant backscattered channel is observed that is associated with complex formation. This channel exhibits a cross-section of approximately 1.4 Å2at a collision energy of 2.65 eV, corresponding to a laboratory ion energy of 5 eV.  相似文献   

11.
The GU miniarray is a ultra high energy cosmic ray (UHECR) detector consisting of eight plastic scintillators of carpet area 2 m2, each viewed by fast PMTs. It is used to detect Giant EAS by the method of time spread measurement of secondary particles produced in the atmosphere. The energies of the air showers have been reestimated using CORSIKA program. As in the original analysis the Cosmic Ray energy was determined via its relation to the ground level parameter Ns, the shower size. This relation was obtained previously through a best fit relation in agreement with QGS model and Yakutsk data. In this work we use CORSIKA code with QGSJET model of high energy hadronic interactions to simulate miniarray data leading to a modified relation between primary energy and shower size. A revised energy spectrum is reported for 1017–1019 eV primary energy.  相似文献   

12.
The evolution of the cosmic ray primary composition in the energy range 106–107 GeV (i.e. the “knee” region) is studied by means of the e.m. and muon data of the Extensive Air Shower EAS-TOP array (Campo Imperatore, National Gran Sasso Laboratories). The measurement is performed through: (a) the correlated muon number (Nμ) and shower size (Ne) spectra, and (b) the evolution of the average muon numbers and their distributions as a function of the shower size. From analysis (a) the dominance of helium primaries at the knee, and therefore the possibility that the knee itself is due to a break in their energy spectrum (at EkHe=(3.5±0.3)×106 GeV) are deduced. Concerning analysis (b), the measurement accuracies allow the classification in terms of three mass groups: light (p,He), intermediate (CNO), and heavy (Fe). At primary energies E0≈106 GeV the results are consistent with the extrapolations of the data from direct experiments. In the knee region the obtained evolution of the energy spectra leads to: (i) an average steep spectrum of the light mass group (γp,He>3.1), (ii) a spectrum of the intermediate mass group harder than the one of the light component (γCNO2.75, possibly bending at EkCNO≈(6–7)×106 GeV), (iii) a constant slope for the spectrum of the heavy primaries (γFe2.3–2.7) consistent with the direct measurements. In the investigated energy range, the average primary mass increases from lnA=1.6–1.9 at E01.5×106 GeV to lnA=2.8–3.1 at E01.5×107 GeV. The result supports the standard acceleration and propagation models of galactic cosmic rays that predict rigidity dependent cut-offs for the primary spectra of the different nuclei. The uncertainties connected to the hadronic interaction model (QGSJET in CORSIKA) used for the interpretation are discussed.  相似文献   

13.
We have used Monte Carlo simulations to investigate the capabilities of a giant air shower observatory designed to detect showers initiated by cosmic rays with energies exceeding 1019 eV. The observatory is to consist of an array of detectors that will characterise the air shower at ground level, and optical detectors to measure the fluorescence light emitted by the shower in the atmosphere. Using these detectors together in a ‘hybrid’ configuration, we find that precise geometrical reconstruction of the shower axis is possible, leading to excellent resolution in energy. The technique is also shown to provide very good reconstruction below 1019 eV, at energies where the ground array is not fully efficient.  相似文献   

14.
Data taken with ten Cosmic Ray Tracking (CRT) detectors and the HEGRA air-shower array on La Palma, Canary Islands, have been analysed to investigate changes of the cosmic ay mass composition at the ‘knee’ of the cosmic-ray flux spectrum near 1015 eV energy. The analysis is based on the angular distributions of particles in air showers. HEGRA data provided the shower size, direction, and core position and CRT data the particle track information. It is shown that the angular distribution of muons in air showers is sensitive to the composition over a wide range of shower sizes and, thus, primary cosmic-ray energies with little systematic uncertainties. Results can be easily expressed in terms of ln A of primary cosmic rays. In the lower part of the energy range covered, we have considerable overlap with direct composition measurements by the JACEE collaboration and find compatible results in the observed rise of ln A. Above about 1015 eV energy we find no or at most a slow further rise of ln A. Simple cosmic-ray composition models are presented which are fully consistent with our results as well as the JACEE flux and composition measurements and the flux measurements of the Tibet ASγ collaboration. Minimal three-parameter composition models defined by the same power-law slope of all elements below the knee and a common change in slope at a fixed rigidity are inconsistent with these data.  相似文献   

15.
The chemical composition of primary cosmic rays with energies from 1015 to 1016.5 eV, so called “knee” region, is examined. We have observed the time structures of air Čerenkov light associated with air showers at Mt. Chacaltaya, Bolivia, since 1995. The distribution of a parameter that characterizes the observed time structures is compared with that calculated with a Monte Carlo technique for various chemical compositions. Then the energy dependence of the average logarithmic mass numbers ln A of the primary cosmic rays is determined. The present result at 1015.3 eV is almost consistent with the result of JACEE (A12) and shows gradual increase in ln A as a function of the primary energy (A24 at 1016 eV). Form the comparison of the observational results with several theoretical models, we conclude that the supernova explosion of massive stars is a plausible candidate for the origin of cosmic rays around the “knee” region.  相似文献   

16.
We have done extensive Monte Carlo simulations using the new simulation codes of CORSIKA and COSMOS to compare with the gamma-family data obtained at Mts. Fuji (3750 m above sea level) and Kanbala (5500 m above sea level). Then, we estimated the primary proton and helium spectra around the knee energy region using a multiple-layered feed-forward neural network as a classifier of primary particle kind. The selection efficiency of proton-induced family events is estimated to be 82%. The flux value of protons at 2×1015 eV is (5.5±1.5)×10−14 (m−2 s−1 sr−1 GeV−1). The result suggests heavy-enriched primary composition around the knee region.  相似文献   

17.
An analysis has been made of the fraction of ultra high energy cosmic rays (above 1018 eV) which could be due to processes involved in two possible ‘Models’. The first is the Giant Magnetic Halo Model and the second is the Dark Matter Halo Model. We find that the former, in which heavy nuclei are trapped in a giant halo, fails for energies above about 3 × 1019 eV. For the Dark Matter Halo Model, in which relic particles follow the “conventional” dark matter and whose decays give ultra high energy cosmic rays, the predicted anisotropies are much higher than those observed. The lack of observation of a finite flux from the Andromeda Galaxy means that the conclusion is insensitive to the spatial scale size of the assumed halo distribution. It is concluded that less than 10% of the ultra high energy cosmic rays come from relic particles in the Galactic halo.  相似文献   

18.
If neutrinos have mass, we give reasons for a possible pattern of three (squaed) mass eigenvalues: m12 (2.8−5.8) (eV)2, m22 0.01 (eV)2, m32 (1.5−1) × 10−4 (eV)2. The flavor states νμ and νe are mixtures of the eigenstates with m2 and m3 with a significant mixing, corresponding to an effective mixing angle of about 0.45. The ντ is nearly the state with m1; the other two effective mixing angles are about an order of magnitude smaller than 0.45. There is a marked similarity to mixing in the quark sector.  相似文献   

19.
Angular correlations of ultra-high energy cosmic rays with cosmologically distant sources may provide clues to these mysterious events. We compare cosmic ray tracks with energies above 1020 eV to a compilation of radio-loud compact QSO positions. The statistical method emphasizes invariant quantities and a test of statistical independence of track and source distributions. Statistical independence is ruled out by several independent statistics at confidence levels of orders 97–99%, indicating that track directions and QSO source positions are correlated at a significant level.  相似文献   

20.
In previous papers (A.D. Erlykin, A.W. Wolfendale, Astropart. Phys. 7 (1997) 1, 203; 8 (1998) 265; J. Phys. G 23 (1997) 979), we presented evidence for structure in the size spectrum of cosmic ray air showers which we interpreted as due to the presence of oxygen and iron nuclei from a local, recent, supernova remnant. Although the energies in question are 3 × 1015 eV and 1.2 × 1016 eV, well above those where direct measurements are possible, the direct measurements are, in fact, relevant. We find that the direct measurements are quite consistent with an extrapolation back of our spectra. Indeed, taken alone, the direct measurements themselves provide strong evidence for the existence of an extra, single source contribution to the total energy spectrum. The paper also includes a discussion of the high energy electron spectrum, anisotropies and the likely site of the local SNR.  相似文献   

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