Inferred Cosmic-Ray Spectrum from Fermi Large Area Telescopeγ-Ray Observations of Earth’s Limb
Physical Review Letters(2014)
摘要
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.Received 13 December 2013DOI:https://doi.org/10.1103/PhysRevLett.112.151103© 2014 American Physical Society
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关键词
observations,spectrum,cosmic-ray
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