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

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

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

Radio emission of air showers with extremely high energy measured by the Yakutsk radio array

The Yakutsk Array is designed to study cosmic rays at energy 10$^{15}$-10$^{20}$ eV. It consists several independent arrays that register charged particles, muons with energy E$\geq$1 GeV, Cherenkov light and radio emission. The paper presents a technical description of the Yakutsk Radio Array and some preliminary results obtained from measurements of radio emission at 30-35 MHz frequency induced by air shower particles with energy $\varepsilon$ $\geq$ 1$\cdot$10$^{17}$ eV. The data obtained at the Yakutsk array in 1986-1989 (first set of measurements) and 2009-2014 (new set of measurements). Based on the obtained results we determined: Lateral distribution function (LDF) of air showers radio emission with energy $\geq$ 10$^{17}$ eV. Radio emission amplitude empirical connection with air shower energy. Determination of depth of maximum by the ratio of amplitude at different distances from the shower axis. For the first time, at the Yakutsk array, radio emission from the air shower with energy $>$ 10$^{19}$ eV was registered including the shower with the highest energy ever registered at the Yakutsk array with energy $\sim$2 $\cdot$ 10$^{20}$ eV.Comment: 11 pages, 20 figures, 2 tables, accepted for publication in NIM A. arXiv admin note: text overlap with arXiv:1609.0327

The energy spectrum of cosmic rays above 10^15 eV as derived from air Cherenkov light measurements in Yakutsk

The Yakutsk array observes the Cherenkov light emitted by UHECR in atmosphere. Recently, an autonomous subarray is added consisting of photomultipliers to measure the showers in the knee region. Our aim is to analyze the combined data set in order to derive the cosmic ray spectrum in the energy range as wide as possible using the same technique. The advantage of the air Cherenkov light measurement is the model independent estimation of the EAS primary energy using the total light flux emitted in the atmosphere. A set of the light lateral distributions observed in the extended energy range is presented also.Comment: 11 pages, 5 figures, submitted to Nuclear Physics B (Proceedings Supplements

Fluctuations of the depth of maximum in extensive air showers and cross-section of p-air inelastic interaction for energy range 10^15-10^17 eV

We present estimation of proton-air inelastic interaction cross-section obtained for different energy values are. Results are compared with different hadron interaction models.Comment: Proc. 32nd ICRC, Aug. 11-18, Beijing, Chin

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

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

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

Enhancement of the Yakutsk array by atmospheric Cherenkov telescopes to study cosmic rays above 101510^{15} eV

The aim of the Yakutsk array enhancement project is to create an instrument to study the highest-energy galactic cosmic rays (CRs) -- their sources, energy spectrum, and mass composition. Additionally, there will be unique capabilities for investigations in the transition region between galactic and extragalactic components of CRs. Using the well-developed imaging atmospheric Cherenkov telescope technique adapted to the energy region $E>10^{15}$ eV, we plan to measure the longitudinal structure parameters of the shower, e.g., angular and temporal distributions of the Cherenkov signal related to $X_{max}$ and the mass composition of CRs. The main advantages of the Yakutsk array, such as its multi-component measurements of extensive air showers, and model-independent CR energy estimation based on Cherenkov light measurements, will be inherited by the instrument to be created.Comment: Proceedings of ECRS-2010, Turku; submitted to ASTRA (Astrophys. Space Sci. Trans