Composition of cosmic rays accelerated in active galactic nuclei

Abstract

The composition of the overall spectrum of cosmic rays (CRs) is studied under the assumption that ultra high energy CRs above the energy 10^{17} eV are produced at the shock created by the expanding cocoons around active galactic nuclei (AGNs). It is shown that the expected CR composition is characterised by two peaks in the energy dependence of the mean CR atomic number <A(ε)>. The first one at the energy ε\approx 10^{17} eV corresponds to the very end of the Galactic CR component, produced in supernova remnants (SNRs). It is followed by a sharp decrease of <A(ε)> within the energy interval from 10^{17} to 10^{18} eV. This is a signature of the transition from Galactic to extragalactic CRs. The second peak, with <ln A> \approx 2, at energy ε\approx 10^{19} eV, expected at the beginning of the GZK cutoff, is the signature of the CR production by the nonrelativistic cocoon shocks. The calculated CR composition is consistent with the existing data. The alternative scenario, which suggests reacceleration increasing the energy of CRs produced in SNRs by a factor of 30, is also examined.

4 pages, 3 figures, accepted for publication in ApJ Letters

References in corpus (7)

• Correlation of the highest energy cosmic rays with nearby extragalactic objects
• Observation of the suppression of the flux of cosmic rays above 4x10^19eV
• Spectrum of cosmic rays, produced in supernova remnants
• The UHECR spectrum measured at the Pierre Auger Observatory and its astrophysical implications
• Cosmic rays from active galactic nuclei
• Observation of the GZK Cutoff Using the HiRes Detector
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Cited by in corpus (6)

• Measurements of the Cosmic Ray Composition with Air Shower Experiments
• Cosmic Ray Acceleration by a Versatile Family of Galactic Wind Termination Shocks
• Measurement of the cosmic-ray energy spectrum above $10^{16}$ eV with the LOFAR Radboud Air Shower Array
• Comparing the energy spectra of ultra-high energy cosmic rays measured with EAS arrays
• Neutrinos and cosmic rays
• A method to search for correlations of ultra-high energy cosmic ray masses with the large scale structures in the local galaxy density field