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Register a new userSpectrum of cosmic rays with energy above $10^{17}$ eV
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There are some discrepancies in the results on energy spectrum from Yakutsk, AGASA, and HiRes experiments. In this work differential energy spectrum of primary cosmic rays based on the Yakutsk EAS Array data is presented. For the largest events values of $S_{600}$ and axes coordinates have been obtained using revised lateral distribution function. Simulation of converters response at large distances showed no considerable underestimation of particle density. Complex shape of spectrum in region of $E > 10^{17}$ eV is confirmed. After adjustment of parameters and additional exposition at the Yakutsk array there are three events with energy $E > 10^{20}$ eV.
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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.
We report a measurement of the energy spectrum of cosmic rays above $2.5{times} 10^{18}$ eV based on $215,030$ events. New results are presented: at about $1.3{times} 10^{19}$ eV, the spectral index changes from $2.51 pm 0.03 textrm{ (stat.)} pm 0.05 textrm{ (sys.)}$ to $3.05 pm 0.05 textrm{ (stat.)}pm 0.10textrm{ (sys.)}$, evolving to $5.1pm0.3textrm{ (stat.)} pm 0.1textrm{ (sys.)}$ beyond $5{times} 10^{19}$ eV, while no significant dependence of spectral features on the declination is seen in the accessible range. These features of the spectrum can be reproduced in models with energy-dependent mass composition. The energy density in cosmic rays above $5{times} 10^{18}$ eV is $(5.66 pm 0.03 textrm{ (stat.)} pm 1.40 textrm{ (sys.)} ) {times} 10^{53}~$erg Mpc$^{-3}$.
Fermi bubbles are giant gamma-ray structures extended north and south of the Galactic center with characteristic sizes of order of 10 kpc recently discovered by Fermi Large Area Telescope. Good correlation between radio and gamma-ray emission in the region covered by Fermi bubbles implies the presence of high-energy electrons in this region. Since it is relatively difficult for relativistic electrons of this energy to travel all the way from the Galactic sources toward Fermi bubbles one can assume that they accelerated in-situ. The corresponding acceleration mechanism should also affect the distribution of the relativistic protons in the Galaxy. Since protons have much larger lifetimes the effect may even be observed near the Earth. In our model we suggest that Fermi bubbles are created by acceleration of electrons on series of shocks born due to periodic star accretions by supermassive black hole Sgr A*. We propose that hadronic CR within the knee of the observed CR spectrum are produced by Galactic supernova remnants distributed in the Galactic disk. Reacceleration of these particles in the Fermi Bubble produces CRs beyond the knee. This model provides a natural explanation of the observed CR flux, spectral indexes, and matching of spectra at the knee.
The energy reconstruction of extensive air showers measured with the LOFAR Radboud Air Shower Array (LORA) is presented in detail. LORA is a particle detector array located in the center of the LOFAR radio telescope in the Netherlands. The aim of this work is to provide an accurate and independent energy measurement for the air showers measured through their radio signal with the LOFAR antennas. The energy reconstruction is performed using a parameterized relation between the measured shower size and the cosmic-ray energy obtained from air shower simulations. In order to illustrate the capabilities of LORA, the all-particle cosmic-ray energy spectrum has been reconstructed, assuming that cosmic rays are composed only of protons or iron nuclei in the energy range between $sim2times10^{16}$ and $2times10^{18}$ eV. The results are compatible with literature values and a changing mass composition in the transition region from a galactic to an extragalactic origin of cosmic rays.
Cosmic rays are the highest energy particles found in nature. Measurements of the mass composition of cosmic rays between 10^{17} eV and 10^{18} eV are essential to understand whether this energy range is dominated by Galactic or extragalactic sources. It has also been proposed that the astrophysical neutrino signal comes from accelerators capable of producing cosmic rays of these energies. Cosmic rays initiate cascades of secondary particles (air showers) in the atmosphere and their masses are inferred from measurements of the atmospheric depth of the shower maximum, Xmax, or the composition of shower particles reaching the ground. Current measurements suffer from either low precision, or a low duty cycle and a high energy threshold. Radio detection of cosmic rays is a rapidly developing technique, suitable for determination of Xmax with a duty cycle of in principle nearly 100%. The radiation is generated by the separation of relativistic charged particles in the geomagnetic field and a negative charge excess in the shower front. Here we report radio measurements of Xmax with a mean precision of 16 g/cm^2 between 10^{17}-10^{17.5} eV. Because of the high resolution in $Xmax we can determine the mass spectrum and find a mixed composition, containing a light mass fraction of ~80%. Unless the extragalactic component becomes significant already below 10^{17.5} eV, our measurements indicate an additional Galactic component dominating at this energy range.
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