Abstract
The experimental data on the cosmic ray energy spectrum obtained from the Small Cherenkov Array in Yakutsk on the measurement of Cherenkov radiation in showers with energy 1015 –1018 eV are discussed. The data were obtained by means of continuous array operation since 1994. The all particle spectrum in this energy region was found to have a complex shape and cannot be described by a simple exponential function with a single slope indicator, g. After the first kink at energy 3 · 1015 eV (knee), the spectrum becomes steeper at Δγ = 0.4 up to energy eV, then part of the spectrum becomes flat to >8 · 1016 eV, the slope of the spectrum is 2.92 ± 0.03 and then again changes slope by Δγ = 0.32 ± 0.05 from about ∼2· 1017 eV. The second kink in the spectrum observed at the Yakutsk EAS array at ∼2·1017 eV, or also called second knee, is a significant result for space astrophysics of ultra-high cosmic rays. In this paper we discuss possible scenarios for spectrum formation of cosmic rays by galactic sources to energies eV, mainly supernovae remnants (SNR) and Metagalactic origins in the energy range 1017 –1018 eV. Most likely, that measurement of the second knee is related with the transitional region, galactic to extragalactic origin of cosmic rays.
Highlights
From the data obtained at the Yakutsk Small Cherenkov array from 1994 to 2014 and selected using the criteria described above, we evaluated the frequency of extensive air showers (EAS) events registered in a given energy range, δE, and zenith angle, θi, per unit of effective area of the Small Cherenkov array
The cosmic ray spectrum cut off due to iron nuclei leaving beyond the galaxy according to the Peters cycle [4] for a given magnetic field rigidity Rc should be observed at the cutoff energy Ec = 26eRc, i.e. at ∼8·1016 eV
A little difference in slope γ23 can be explained by cosmic ray injection from metagalactic sources [11], and some compensation of a dramatic change of slope at the break point in the energy range 5·1016–3·1018 eV by protons and lighter nuclei from metagalaxy
Summary
The main objectives of cosmic ray (CR) research of ultra-high energies are to determine the anisotropy of the energy spectrum and chemical composition of the primary CR particles. The main Yakutsk EAS array consists of small arrays with equipment designed to perform both general and specific objectives, such as the measurement of muons by the Large Muon Detector, the measurement of the profile of the cascade curve system by Cherenkov detectors, measurement of radio emission, monitoring of the atmosphere during the registration period of air showers etc. This equipment is controlled by a system of computers connected in a local network [1]. One of the tasks that had to be settled was to study the spectrum of cosmic rays (CR) in the energy range 1015–1017 eV [3], where, according to [4], the manifestation of the fine structure in the spectrum of CR due to the interaction of cosmic ray particles with the magnetic field of the Galaxy was expected
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