Inferred Cosmic-Ray Spectrum from Fermi Large Area Telescope gamma-Ray Observations of Earth's Limb
2014 (English)In: Physical Review Letters, ISSN 0031-9007, Vol. 112, no 15, 151103- p.Article in journal (Refereed) Published
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 Earth's limb for an indirect measurement of the local spectrum of CR protons in the energy range similar to 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 similar to 200 GeV, respectively.
Place, publisher, year, edition, pages
2014. Vol. 112, no 15, 151103- p.
IdentifiersURN: urn:nbn:se:su:diva-104151DOI: 10.1103/PhysRevLett.112.151103ISI: 000334597300003OAI: oai:DiVA.org:su-104151DiVA: diva2:722632