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Inferred cosmic-ray spectrum from Fermi large area telescope γ-ray observations of Earth's limb.

  • Author(s): Ackermann, M
  • Ajello, M
  • Albert, A
  • Allafort, A
  • Baldini, L
  • Barbiellini, G
  • Bastieri, D
  • Bechtol, K
  • Bellazzini, R
  • Blandford, RD
  • Bloom, ED
  • Bonamente, E
  • Bottacini, E
  • Bouvier, A
  • Brandt, TJ
  • Brigida, M
  • Bruel, P
  • Buehler, R
  • Buson, S
  • Caliandro, GA
  • Cameron, RA
  • Caraveo, PA
  • Cecchi, C
  • Charles, E
  • Chaves, RCG
  • Chekhtman, A
  • Chiang, J
  • Chiaro, G
  • Ciprini, S
  • Claus, R
  • Cohen-Tanugi, J
  • Conrad, J
  • Cutini, S
  • Dalton, M
  • D'Ammando, F
  • de Angelis, A
  • de Palma, F
  • Dermer, CD
  • Digel, SW
  • Di Venere, L
  • do Couto e Silva, E
  • Drell, PS
  • Drlica-Wagner, A
  • Favuzzi, C
  • Fegan, SJ
  • Ferrara, EC
  • Focke, WB
  • Franckowiak, A
  • Fukazawa, Y
  • Funk, S
  • Fusco, P
  • Gargano, F
  • Gasparrini, D
  • Germani, S
  • Giglietto, N
  • Giordano, F
  • Giroletti, M
  • Glanzman, T
  • Godfrey, G
  • Gomez-Vargas, GA
  • Grenier, IA
  • Grove, JE
  • Guiriec, S
  • Gustafsson, M
  • Hadasch, D
  • Hanabata, Y
  • Harding, AK
  • Hayashida, M
  • Hayashi, K
  • Hewitt, JW
  • Horan, D
  • Hou, X
  • Hughes, RE
  • Inoue, Y
  • Jackson, MS
  • Jogler, T
  • Jóhannesson, G
  • Johnson, AS
  • Kamae, T
  • Kawano, T
  • Knödlseder, J
  • Kuss, M
  • Lande, J
  • Larsson, S
  • Latronico, L
  • Longo, F
  • Loparco, F
  • Lovellette, MN
  • Lubrano, P
  • Mayer, M
  • Mazziotta, MN
  • McEnery, JE
  • Mehault, J
  • Michelson, PF
  • Mitthumsiri, W
  • Mizuno, T
  • Moiseev, AA
  • Monte, C
  • Monzani, ME
  • Morselli, A
  • Moskalenko, IV
  • Murgia, S
  • Nemmen, R
  • Nuss, E
  • Ohsugi, T
  • Okumura, A
  • Orienti, M
  • Orlando, E
  • Ormes, JF
  • Paneque, D
  • Panetta, JH
  • Perkins, JS
  • Pesce-Rollins, M
  • Piron, F
  • Pivato, G
  • Porter, TA
  • Rainò, S
  • Rando, R
  • Razzano, M
  • Razzaque, S
  • Reimer, A
  • Reimer, O
  • Ritz, S
  • Roth, M
  • Schaal, M
  • Schulz, A
  • Sgrò, C
  • Siskind, EJ
  • Spandre, G
  • Spinelli, P
  • Strong, AW
  • Takahashi, H
  • Takeuchi, Y
  • Thayer, JG
  • Thayer, JB
  • Thompson, DJ
  • Tibaldo, L
  • Tinivella, M
  • Torres, DF
  • Tosti, G
  • Troja, E
  • Tronconi, V
  • Usher, TL
  • Vandenbroucke, J
  • Vasileiou, V
  • Vianello, G
  • Vitale, V
  • Werner, M
  • Winer, BL
  • Wood, KS
  • Wood, M
  • Yang, Z
  • Fermi LAT Collaboration
  • et al.
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 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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