AI Article Synopsis
- Recent measurements from ATIC-2, CREAM, and PAMELA have revealed unexpected patterns in cosmic-ray proton and helium spectra, showing hardening above several hundred GeV and a gradual softening below this range.
- The findings suggest a harder spectrum for helium compared to protons, which may provide insights into the origins of high-energy cosmic rays.
- Analysis using Fermi Large Area Telescope data indicates that both single and broken power law models fit the local proton spectrum well, with indices around 2.68 and 2.61 for energies above 200 GeV.
Article Abstract
Recent accurate measurements of cosmic-ray (CR) species by ATIC-2, CREAM, and PAMELA reveal an unexpected hardening in the proton and He spectra above a few hundred GeV, a gradual softening of the spectra just below a few hundred GeV, and a harder spectrum of He compared to that of protons. These newly discovered features may offer a clue to the origin of high-energy CRs. We use the Fermi Large Area Telescope observations of the γ-ray emission from Earth's limb for an indirect measurement of the local spectrum of CR protons in the energy range ∼90 GeV-6 TeV (derived from a photon energy range 15 GeV-1 TeV). Our analysis shows that single power law and broken power law spectra fit the data equally well and yield a proton spectrum with index 2.68±0.04 and 2.61±0.08 above ∼200 GeV, respectively.
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| http://dx.doi.org/10.1103/PhysRevLett.112.151103 | DOI Listing |
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