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

Fermi-LAT Collaboration: M. Ackermann , M. Ajello , A. Albert , A. Allafort , L. Baldini , G. Barbiellini , D. Bastieri , K. Bechtol

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R. Bellazzini R. D. Blandford E. D. Bloom E. Bonamente E. Bottacini A. Bouvier T. J. Brandt M. Brigida P. Bruel R. Buehler S. Buson G. A. Caliandro R. A. Cameron P. A. Caraveo C. Cecchi E. Charles R. C. G. Chaves A. Chekhtman J. Chiang G. Chiaro S. Ciprini R. Claus J. Cohen-Tanugi J. Conrad S. Cutini M. Dalton F. D'Ammando A. De Angelis F. de Palma C. D. Dermer S. W. Digel L. Di Venere E. do Couto e Silva P. S. Drell A. Drlica-Wagner C. Favuzzi S. J. Fegan E. C. Ferrara W. B. Focke A. Franckowiak Y. Fukazawa S. Funk P. Fusco F. Gargano D. Gasparrini S. Germani N. Giglietto F. Giordano M. Giroletti T. Glanzman G. Godfrey G. A. Gomez-Vargas I. A. Grenier J. E. Grove S. Guiriec M. Gustafsson D. Hadasch Y. Hanabata A. K. Harding M. Hayashida K. Hayashi J. W. Hewitt D. Horan X. Hou R. E. Hughes Y. Inoue M. S. Jackson T. Jogler G. J\'ohannesson A. S. Johnson T. Kamae T. Kawano J. Kn\"odlseder M. Kuss J. Lande S. Larsson L. Latronico F. Longo F. Loparco M. N. Lovellette P. Lubrano M. Mayer M. N. Mazziotta J. E. McEnery J. Mehault P. F. Michelson W. Mitthumsiri T. Mizuno A. A. Moiseev C. Monte M. E. Monzani A. Morselli I. V. Moskalenko S. Murgia R. Nemmen E. Nuss T. Ohsugi A. Okumura M. Orienti E. Orlando J. F. Ormes D. Paneque J. H. Panetta J. S. Perkins M. Pesce-Rollins F. Piron G. Pivato T. A. Porter S. Rain\`o R. Rando M. Razzano S. Razzaque A. Reimer O. Reimer S. Ritz M. Roth M. Schaal A. Schulz C. Sgr\`o E. J. Siskind G. Spandre P. Spinelli A. W. Strong H. Takahashi Y. Takeuchi J. G. Thayer J. B. Thayer D. J. Thompson L. Tibaldo M. Tinivella D. F. Torres G. Tosti E. Troja V. Tronconi T. L. Usher J. Vandenbroucke V. Vasileiou G. Vianello V. Vitale M. Werner B. L. Winer K. S. Wood M. Wood Z. Yang

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keywords spectrumspectraabovecosmic-rayearthenergyfermigamma

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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 $\gamma$-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.

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

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