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Cosmic-ray energy spectrum and composition up to the ankle: the case for a second Galactic component
Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Radboud Univ Nijmegen, Netherlands.
Radboud Univ Nijmegen, Netherlands.
Radboud Univ Nijmegen, Netherlands.
Radboud Univ Nijmegen, Netherlands.
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2016 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 595, A33Article in journal (Refereed) Published
Abstract [en]

Motivated by the recent high-precision measurements of cosmic rays by several new-generation experiments, we have carried out a detailed study to understand the observed energy spectrum and composition of cosmic rays with energies up to about 10(18) eV. Our study shows that a single Galactic component with subsequent energy cut-offs in the individual spectra of different elements, optimised to explain the observed elemental spectra below similar to 10(14) eV and the "knee" in the all-particle spectrum, cannot explain the observed all-particle spectrum above similar to 2 x 10(16) eV. We discuss two approaches for a second component of Galactic cosmic rays re-acceleration at a Galactic wind termination shock, and supernova explosions of Wolf-Rayet stars, and show that the latter scenario can explain almost all observed features in the all-particle spectrum and the composition up to similar to 10(18) eV, when combined with a canonical extra-galactic spectrum expected from strong radio galaxies or a source population with similar cosmological evolution. In this two-component Galactic model, the knee at similar to 3 x 10(15) eV and the "second knee" at similar to 10(17) eV in the all-particle spectrum are due to the cut-offs in the first and second components, respectively. We also discuss several variations of the extra-galactic component, from a minimal contribution to scenarios with a significant component below the "ankle" (at similar to 4 x 10(18) eV), and find that extragalactic contributions in excess of regular source evolution are neither indicated nor in conflict with the existing data. We also provide arguments that an extra-galactic contribution is unlikely to dominate at or below the second knee. Our main result is that the second Galactic component predicts a composition of Galactic cosmic rays at and above the second knee that largely consists of helium or a mixture of helium and CNO nuclei, with a weak or essentially vanishing iron fraction, in contrast to most common assumptions. This prediction is in agreement with new measurements from LOFAR and the Pierre Auger Observatory which indicate a strong light component and a rather low iron fraction between similar to 10(17) and 10(18) eV.

Place, publisher, year, edition, pages
2016. Vol. 595, A33
Keyword [en]
diffusion, stars: winds, outflows, ISM: supernova remnants, galaxies: ISM, cosmic rays
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
URN: urn:nbn:se:lnu:diva-59468DOI: 10.1051/0004-6361/201628894ISI: 000388573500090OAI: oai:DiVA.org:lnu-59468DiVA: diva2:1059751
Available from: 2016-12-23 Created: 2016-12-23 Last updated: 2016-12-23Bibliographically approved

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Thoudam, Satyendra
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Citation style
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