On the cause of variability of the cosmic ray spectrum in the knee region
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On the Cause of Variability of the Cosmic Ray Spectrum in the Knee Region V. M. Loznikova, N. S. Erokhina, b*, N. N. Zol’nikovaa, and L. A. Mikhailovskayaa a Space
Research Institute, Russian Academy of Sciences, Moscow, 117997 Russia Friendship University of Russia, Moscow, 117198 Russia *e-mail: [email protected]
b Peoples’
Received February 1, 2017
Abstract—Cosmic ray (CR) energy spectra for H, He, Si, and Fe nuclei with energy-to-charge number ratios %/Z in the range from 10 to 5 × 107 GeV are studied using observational data obtained at different times in different energy ranges: AMS-02, CREAM, Tibet ASγ, Tibet (hybrid), GRAPES-3, KASCADE, and KASCADE-Grande. Comparison of the H and He CR fluxes according to the KASCADE and KASCADE-Grande data (for different models of deconvolving CR spectra) with the Tibet ASγ and Tibet (hybrid) data obtained at another time in the range of %/Z ~ 3 × 106 GeV demonstrates space weather-caused variability of the CR flux. This feature of CR energy spectra in the Tibet ASγ data is most clearly observed in the spectra of heavier nuclei (Si and Fe) according to the KASCADE-Grande and GRAPES-3 data. The variability in the energy spectra of all CRs in the vicinity of the “knee” is shown in the data of Yakutsk EAS, CASA-BLANCA, and Tibet-III experiments. The variability of the CR flux on a time scale on the order of several years exists only if the source corresponding to the peak in the energy spectrum is situated at a distance of no more than 1 pc from the Sun. Rapid surfatron acceleration of CRs may result from colliding interstellar clouds nearest to the Sun (LIC and G). This acceleration mechanism allows one to explain the variability of the CR spectrum in the range 103 GeV < %/Z < 108 GeV. Conditions for the trapping of strongly relativistic Fe nuclei by an electromagnetic wave, the dynamics of the components of the particle velocity and momentum, and the dependence of the particle acceleration rate on the initial parameters of the problem are analyzed using numerical calculations. The structure of the phase plane of the accelerated Fe nuclei is examined. Optimal conditions for the implementation of ultrarelativistic surfatron acceleration of Fe nuclei by an electromagnetic wave are formulated. DOI: 10.1134/S1063780X17090069
1. INTRODUCTION In [1–4], the dynamics of cosmic ray (CR) energy spectra according to the data from the AMS-02, CREAM, Tibet ASγ, Tibet (hybrid), GRAPES-3, KASCADE, and KASCADE-Grande experiments for H and He nuclei at energy-to-charge number ratios of 103 GeV < %/Z < 106 GeV was compared with numerical studies of the surfatron acceleration mechanism. CRs are accelerated via this mechanism in a constant magnetic field by an electromagnetic wave that is excited by colliding interstellar clouds. In this work, attention is focused on the nucleus energy range corresponding to energy-to-charge number ratios of 105 GeV < %/Z < 107 GeV in the vicinity of the socalled “knee” in the CR energy spectrum. Analysis of the data from the CREAM, Tibet ASγ, and T
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