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Fermi LAT Observation of Diffuse Gamma-Rays Produced Through Interactions between Local Interstellar Matter and High Energy Cosmic Rays

Abdo, A. A. / Ackermann, M. / Ajello, M. / B. Atwood, W. / Axelsson, M. / Baldini, L. / Ballet, J. / Barbiellini, G. / Bastieri, D. / Baughmann, B.M. / Bechtol, K. / Bellazzini, R. / Berenji, B. / Bloom, E.D. / Bonamente, E. / Borgland, A.W. / Bregeon, J. / Brez, A. / Brigida, M. / Bruel, P. / Burnett, T.H. / A. Caliandro, G. / A. Cameron, R. / A. Caraveo, P. / Carlson, P. / Casandjian, J.M. / Cecchi, C. / Celik, O. / Chekhtman, A. / Cheung, C.C. / Ciprini, S. / Claus, R. / Cohen-Tanugi, J. / Conrad, J. / Cutini, S. / Dermer, C.D. / De Angelis, A. / De Palma, F. / Digel, S.W. / Do Couto E Silva, E. / Drell, P.S. / Dubois, R. / Dumora, D. / Farnier, C. / Favuzzi, C. / Fegan, S.J. / Focke, W.B. / Frailis, M. / Fukazawa, Y. / Funk, S. / Fusco, P. / Gargano, F. / Gasparrini, D. / Gehrels, N. / Germani, S. / Giebels, B. / Giglietto, N. / Giordano, F. / Glanzman, T. / Godfrey, G. / Grenier, I.A. / Grondin, M.-H. / Grove, J.E. / Guillemot, L. / Guiriec, S. / Hamada, N. / Harding, A.K. / Hayashida, M. / Hugues, R.E. / Johansson, G. / Johnson, A.S. / Johnson, R.P. / Johnson, W.N. / Kamae, T. / Katagiri, H. / Kawai, N. / Kerr, M. / Knödlseder, J. / Kocian, M. L. / Kuehn, F. / Kuss, M. / Lande, J. / Latronico, L. / Lemoine-Goumard, M. / Longo, F. / Loparco, F. / Lott, B. / Lovellette, M.N. / Lubrano, P. / Makeev, A. / Mazziotta, M.N. / Mcenery, J.E. / Meurer, C. / Michelson, P.F. / Mitthumsiri, W. / Mizuno, T. / Moiseev, A.A. / Monte, C. / Monzani, M.E. / Morselli, A. / Moskalenko, I.V. / Murgia, S. / Nolan, P.L. / Norris, J.P. / Nuss, E. / Ohsugi, T. / Okumura, A. / Omodei, N. / Orlando, E. / Ormes, J.F. / Ozaki, M. / Paneque, D. / Panetta, J.H. / Parent, D. / Pepe, M. / Pesce-Rollins, M. / Piron, F. / Pohl, M. / Porter, T. A. / Rainò, S. / Rando, R. / Razzano, M. / Reimer, A. / Reimer, O. / Reposeur, T. / Ritz, S. / Rochester, L. S. / Rodriguez, A. Y. / Ryde, F. / Sadrosinski, H.F-W. / Sanchez, D. / Sander, A. / Parkinson, P. M. Saz / Schalk, T.L. / Sellerholm, A. / Sgro, G. / Smith, D.A. / Smith, P.D. / Spandre, G. / Spinelli, P. / Starck, Jean-Luc / Stecker, F. W. / Strickman, M. S. / Strong, A.W. / Suson, D. J. / Tajima, H. / Takahashi, H. / Takahashi, T. / Tanaka, T. / Thayer, J.B. / Thayer, J.G. / Thompson, D.J. / Tibaldo, L. / Torres, D. F. / Tosti, G. / Tramacere, A. / Uchiyama, Y. / Usher, T. L. / Vasileiou, V. / Vilchez, N. / Vitale, V. / Waite, A. P. / Wang, P. / Winer, B. L. / Wood, K. S. / Ylinen, T. / Ziegler, M. - 2009
Observations by the Large Area Telescope (LAT) on the \textit{Fermi} mission of diffuse $\gamma$-rays in a mid-latitude region in the third quadrant (Galactic longitude $l$ from $200\arcdeg$ to $260\arcdeg$ and latitude $| b |$ from $22\arcdeg$ to $60\arcdeg$) are reported. The region contains no known large molecular cloud and most of the atomic hydrogen is within 1 kpc of the solar system. The contributions of $\gamma$-ray point sources and inverse Compton scattering are estimated and subtracted. The residual $\gamma$-ray intensity exhibits a linear correlation with the atomic gas column density in energy from 100 MeV to 10 GeV. The measured integrated $\gamma$-ray emissivity is $(1.63 \pm 0.05) \times 10^{-26} {\rm photons s^{-1} sr^{-1} H\mathchar`-atom^{-1}}$ and $(0.66 \pm 0.02) \times 10^{-26} {\rm photons s^{-1} sr^{-1} H\mathchar`-atom^{-1}}$ above 100 MeV and above 300 MeV, respectively, with additional systematic error of $\sim 10%$. The differential emissivity in 100 MeV--10 GeV agrees with calculations based on cosmic ray spectra consistent with those directly measured, at the 10% level. The results obtained indicate that cosmic ray nuclei spectra within 1 kpc from the solar system in regions studied are close to the local interstellar spectra inferred from direct measurements at the Earth within $\sim 10%$.

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