Problem of the energy spectrum of ultrahigh-energy cosmic rays
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EMENTARY PARTICLES AND FIELDS Theory
Problem of the Energy Spectrum of Ultrahigh-Energy Cosmic Rays A. V. Glushkov* Institute of Cosmophysical Research and Aeronomy, Yakutsk Research Center, Siberian Division, Russian Academy of Sciences, pr. Lenina 31, Yakutsk, 677980 Russia Received January 15, 2008; in final form, April 7, 2008
Abstract—A number of cosmic-ray energy spectra measured in the energy region E0 ≥ 1017 eV at the Yakutsk array and at AGASA, Haverah Park, HiRes, Auger, and SUGAR within different periods of time were considered. It was shown that, upon rescaling the energy of these spectra by factors of K = 0.75, 0.85, 0.9, 1.02, 1.19, and 1.29, respectively, all of them agree with one another rather well in shape. The factors K themselves exhibit a pronounced north–south dependence on the geographical latitude of the positions of the above arrays. PACS numbers: 95.30.-k, 96.40.Pq, 96.40.-z, 98.70.-f DOI: 10.1134/S1063778809010116
1. INTRODUCTION
contradicts a steep decrease expected for the spectrum in the region E0 6 × 1019 eV on the basis of the theoretical concepts developed by Greisen [11] and Zatsepin and Kuz’min [12] (GZK cutoff) because of the intense interaction of giant air showers with microwave background radiation. The problem of Greisen–Zatsepin–Kuzmin cutoff gave impetus to creating the new arrays AGASA (Akeno Giant Air Shower Array, Japan) and Fly’s Eye–HiRes (USA), which had a higher sensitivity. Hopes for ultimately solving the problem of the giant-air-shower origin were placed on these arrays, but these hopes proved to be illusory. The supergiant array Auger (its area is 3000 km2 ), commissioned recently in Argentina, brought about some sensational results, reported by the Auger group in the summer of 2007 at the 30th Cosmic Ray Conference in Mexico (for an overview, see [9, 13]), whereupon the situation became still more intriguing. Here, we consider the problem of the energy spectrum of ultrahigh-energy cosmic rays on the basis of all statistically significant results without subjecting them to any selection even if some of them may seem outdated and not quite reliable. This yields a fuller pattern of the very problem of measuring the spectrum and opens some new possibilities for solving it.
The energy spectrum of ultrahigh-energy (E0 1017 eV) cosmic rays is a key link in the chain of involved problems of the origin of primary particles having such energies. Giant air showers (GAS) of limiting energy in the region E0 1019 eV have aroused great interest over almost 40 years—since the discovery of the first events recorded at the largest arrays worldwide such as Volcano Ranch (USA) [1], Haverah Park (England) [2], SUGAR (Australia) [3], and the Yakutsk array [4]. The shape and the intensity of the spectrum are of paramount importance for revealing the composition of primary cosmic rays (PCR) and sources of their formation. The experimental data obtained at the different arrays are markedly different in absolute intensity but are similar in shape. This can clearly be seen in Fig. 1a. T
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