Inferred cosmic-ray spectrum from \it Fermi-LAT γ-ray observations of the Earth's limb

2014/03/21 by LAT Collaboration, Ackermann, M., Ajello, M. +150
#FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE)

paper · doi:10.48550/arxiv.1403.5372

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 \it Fermi Large Area Telescope observations of the γ-ray emission from the 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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