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 \gamma -ray emission from the Earth ’ s limb for an indirect measurement of the local spectrum of CR protons in the energy range \sim 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 \pm 0.04 and 2.61 \pm 0.08 above \sim 200 GeV , respectively .