Muons in EAS with E>=10^17eV according to the data from Yakutsk array

The lateral distribution of muons with threshold energy e ~ 1*sec(theta) GeV have been studied in showers with energy E>=10^17 eV. The data considered in the analysis have been collected from November 2011 to June 2013. Experimental values are compared to predictions obtained with the use of CORSIKA code within the framework of various hadron interaction models. The best agreement between experiment and theory is observed for QGSJETII-04 model. At E~10^17 eV it complies to a mixed cosmic ray composition with the mean atomic number ~3.0+/-0.5. At E>= 4*10^17 eV the composition varies around the value ~0.5.Comment: 12 pages, 7 figure

Mass composition of cosmic rays with energy above 10**17 eV according to surface detectors of the Yakutsk EAS array

We discuss the lateral distribution of charged particles in extensive air showers with energy above $10^{17}$ eV measured by surface scintillation detectors of Yakutsk EAS array. The analysis covers the data obtained during the period from 1977 to 2013. Experimental values are compared to theoretical predictions obtained with the use of CORSIKA code within frameworks of different hadron interaction models. The best agreement between theory and experiment is observed for QGSJet01 and QGSJet-II-04 models. A change in the cosmic ray mass composition towards proton is observed in the energy range $(1-20) \times 10^{17}$ eV.Comment: 5 pages, 4 figure

The depth of maximum shower development and its fluctuations: cosmic ray mass composition at E_0 >= 10^17 eV

We present new data on Cherenkov light observations obtained during the period 1994-2009, after a modernization of the Yakutsk EAS array. A complex analysis of \xmax and its fluctuations \sigma(\xmax) was performed over a wide energy range. With the new data, according to QGSJet II model, an estimation was made of the cosmic ray mass composition for \E \sim 10^{17} - 3 \times 10^{19} eV. The result points towards a mixed composition with a large portion of heavy nuclei at \E \sim 10^{17} eV and the dominance of light nuclei at \E \sim 10^{19} eV. The analysis of \sigma(\xmax) energy dependence for the same energies qualitatively confirms this result. The shape of the \xmax distribution at fixed energy $10^{18}$ eV is analysed to make more precise conclusions on cosmic ray mass composition.Comment: Contributed paper to the XVI International Symposium on Very High Energy Cosmic Ray Interactions ISVHECRI 2010, Batavia, IL, USA (28 June - 2 July 2010). 4 pages, 5 figure

Revision of the energy calibration of the Yakutsk EAS array

Responses of surface and underground scintillation detectors of Yakutsk array are calculated for showers initiated by primary particles with energy E0>=1.0E17 eV within the frameworks of QGSJet01 QGSIIJet-II-04, SIBYLL-2.1 and EPOS-LHC hadron interaction models. A new estimation of E0 is obtained with the use of various methods. The resulting energy is lower compared to the obtained with earlier method by factor ~1.33.Comment: 15 pages, 5 figure

The nature of pulses delayed by 5 mcs in scintillation detectors from showers with the energy above 1E17 eV

Here we consider EAS events with energy above 1E17 eV with recorded pulses delayed by t>=5 mcs in scintillation detectors with different thresholds: 10, 5 and 1.8 MeV. In order to identify pulses from electrons, muons and neutrons, experimental data were compared to computational results performed within the framework of QGSJET01d model. Preliminary, one may speculate of registration of low-energy electrons arisen from moderation of neutrons in a detector or a medium surrounding a detector or in the snow cover and frozen crust (albedo particles). The fact that such pulses were registered mostly in low-threshold detectors confirms this hypothesis.Comment: Proc. of the 33rd ICRC (2013), Rio de Janeiro, Brazi

Spectrum and mass composition of cosmic rays in the energy range 10^15-10^18 eV derived from the Yakutsk array data

A spectrum of cosmic rays within energy range 10^15 - 3x10^17 eV was derived from the data of the small Cherenkov setup, which is a part of the Yakutsk complex EAS array. In this, work a new series of observation is covered. These observations lasted from 2000 till 2010 and resulted in increased number of registered events within interval 10^16 - 10^18 eV, which in turn made it possible to reproduce cosmic ray spectrum in this energy domain with better precision. A sign of a thin structure is observed in the shape of the spectrum. It could be related to the escape of heavy nuclei from our Galaxy. Cosmic ray mass composition was obtained for the energy region 10^16 - 10^18 eV. A joint analysis of spectrum and mass composition of cosmic rays was performed. Obtained results are considered in the context of theoretical computations that were performed with the use of hypothesis of galactic and meta-galactic origin of cosmic rays.Comment: Proc. 32nd ICRC, Aug.11-18, Beijing, Chin

Large-scale distribution of cosmic rays in right ascension as observed by the Yakutsk array at energies above 101810^{18} eV

We present the results of searches for anisotropy in the right ascension ($RA$) distribution of arrival directions of cosmic rays (CRs) detected with the Yakutsk array during the 1974--2008 observational period in the energy range above $10^{18}$ eV. Two methods of analysis are applied to two sub-samples of the data. Particularly, estimations of the first and second harmonic amplitudes are given, as well as the first harmonic phase in adjacent energy intervals. Analysis of variance demonstrates a significant contraction of the minimal width of the $RA$ distribution in the energy bin $(10^{19},1.78\times10^{19})$ eV with respect to the isotropic distribution, which may be attributed to a possible source of CRs within the interval $RA\in(15^0,45^0)$.Comment: 8 pages, 6 figures, 2 tables, accepted for publication in Astroparticle Physic

The Relation Between Charged Particles and Muons With Threshold Energy 1 GeV in Extensive Air Showers Registered at the Yakutsk EAS Array

Characteristics of the muon component in EAS are analyzed together with their fluctuations. The aim of this analysis -- a comparison of experimental data with computational results obtained within frameworks of various hadron interaction models for protons and iron nuclei and an estimation of cosmic ray mass composition in the ultra-high energy region.Comment: Contributed paper to the XVI International Symposium on Very High Energy Cosmic Ray Interactions (ISVHECRI 2010), Batavia, IL, USA, 28 June - 2 July 201

Behavior of some characteristics of EAS in the region of knee and ankle of spectrum

The energy dependence of such characteristics as a ratio of the total number of charged particles to the total flux of EAS Cherenkov radiation, a ratio of E(thr)>=1GeV muon flux density at the distance of 600m from a shower core to charged particle flux density, a ratio of the energy transferred to the electromagnetic component of EAS to the primary particle energy is presented. Their comparison with two-component mass composition of cosmic rays (p-Fe) in the framework of calculations by a QGSJET model is given.Comment: 6 pages, 9 figure

Average mass composition of primary cosmic rays in the superhigh energy region by Yakutsk complex EAS array data

The characteristics relating to the lateral and longitudinal development of EAS in the energy region of 10^15-10^19eV have been analyzed in the framework of the QGSJET model and of mass composition of primary cosmic rays. It is found that at E(0) >= 5*10^15eV the mean mass composition of primary cosmic rays begins to vary as indicated by a rise of with increasing energy. The maximum value of is observed at E(0) ~ (5-50)*10^16eV. It is confirmed by data of many compact EAS arrays and does not contradict an anomalous diffusion model of cosmic ray propagation in our Galaxy. In the superhigh energy region (>=10^18eV) the value begins to decrease, i.e. the mass composition becomes lighter and consists of protons and nuclei of He and C. It does not contradict our earlier estimations for the mass composition and points to a growing role of the metagalactic component of cosmic rays in the superhigh energy region.Comment: 5 pages, 2 figure