- Main
Inferred cosmic-ray spectrum from Fermi large area telescope γ-ray observations of Earth's limb.
- Ackermann, M;
- Ajello, M;
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- Allafort, A;
- Baldini, L;
- Barbiellini, G;
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- Mayer, M;
- Mazziotta, MN;
- McEnery, JE;
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- Mitthumsiri, W;
- Mizuno, T;
- Moiseev, AA;
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- Monzani, ME;
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- Moskalenko, IV;
- Murgia, S;
- Nemmen, R;
- Nuss, E;
- Ohsugi, T;
- Okumura, A;
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- Orlando, E;
- Ormes, JF;
- Paneque, D;
- Panetta, JH;
- Perkins, JS;
- Pesce-Rollins, M;
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- Pivato, G;
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- Fermi LAT Collaboration
- et al.
Published Web Location
https://doi.org/10.1103/physrevlett.112.151103Abstract
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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