%0 Journal Article
%T GAMMA-RAY OBSERVATIONS OF THE ORION MOLECULAR CLOUDS WITH THE FERMI LARGE AREA TELESCOPE
%+ Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112))
%+ Institut de recherche en astrophysique et planétologie (IRAP)
%+ Laboratoire Leprince-Ringuet (LLR)
%+ Laboratoire Univers et Particules de Montpellier (LUPM)
%+ GLAST
%A Ackermann, Markus
%A Ajello, Marco
%A Allafort, A.
%A Antolini, E.
%A Baldini, Luca
%A Ballet, Jean
%A Barbiellini, Guido
%A Bastieri, D.
%A Bechtol, K.
%A Bellazzini, R.
%A Berenji, B.
%A D. Blandford, R.
%A D. Bloom, E.
%A Bonamente, E.
%A W. Borgland, A.
%A Bottacini, E.
%A J. Brandt, T.
%A Bregeon, J.
%A Brigida, M.
%A Bruel, Pascal
%A Buehler, R.
%A Buson, S.
%A A. Caliandro, G.
%A A. Cameron, R.
%A Caraveo, P. A.
%A Cecchi, C.
%A Chekhtman, A.
%A Chiang, J.
%A Ciprini, S.
%A Claus, R.
%A Cohen-Tanugi, J.
%A Conrad, J.
%A d'Ammando, F.
%A de Angelis, A.
%A de Palma, F.
%A D. Dermer, C.
%A Do Couto E Silva, E.
%A S. Drell, P.
%A Drlica-Wagner, A.
%A Enoto, T.
%A Falletti, L.
%A Favuzzi, C.
%A J. Fegan, S.
%A C. Ferrara, E.
%A B. Focke, W.
%A Fukazawa, Y.
%A Fukui, Y.
%A Fusco, P.
%A Gargano, F.
%A Gasparrini, D.
%A Germani, S.
%A Giglietto, N.
%A Giordano, F.
%A Giroletti, M.
%A Glanzman, T.
%A Godfrey, G.
%A Guiriec, S.
%A Hadasch, D.
%A Hanabata, Y.
%A K. Harding, A.
%A Hayashida, M.
%A Hayashi, K.
%A Horan, D.
%A Hou, X.
%A E. Hughes, R.
%A S. Jackson, M.
%A J 'Ohannesson, G.
%A S. Johnson, A.
%A Kamae, T.
%A Katagiri, H.
%A Kataoka, J.
%A Kerr, M.
%A Knödlseder, Jürgen
%A Kuss, M.
%A Lande, J.
%A Larsson, S.
%A Lee, S.-H.
%A Longo, F.
%A Loparco, F.
%A N. Lovellette, M.
%A Lubrano, P.
%A Makishima, K.
%A N. Mazziotta, M.
%A Mehault, J.
%A Mitthumsiri, W.
%A A. Moiseev, A.
%A Monte, C.
%A E. Monzani, M.
%A Morselli, A.
%A V. Moskalenko, I.
%A Murgia, S.
%A Nakamori, T.
%A Naumann-Godo, M.
%A Nishino, S.
%A P. Norris, J.
%A Nuss, E.
%A Ohno, M.
%A Ohsugi, T.
%A Okumura, A.
%A Orienti, M.
%A Orlando, E.
%A F. Ormes, J.
%A Ozaki, M.
%A Paneque, D.
%A H. Panetta, J.
%A Parent, D.
%A Pelassa, V.
%A Pesce-Rollins, M.
%A Pierbattista, M.
%A Piron, F.
%A Pivato, G.
%A Porter, T.A.
%A Rain'O, S.
%A Razzano, M.
%A Reimer, A.
%A Reimer, O.
%A Roth, M.
%A F.-W. Sadrozinski, H.
%A Sgr'O, C.
%A J. Siskind, E.
%A Spandre, G.
%A Spinelli, P.
%A W. Strong, A.
%A Takahashi, H.
%A Takahashi, T.
%A Tanaka, T.
%A G. Thayer, J.
%A B. Thayer, J.
%A Tibolla, O.
%A Tinivella, M.
%A F. Torres, D.
%A Tramacere, A.
%A Troja, E.
%A Uchiyama, Y.
%A L. Usher, T.
%A Vandenbroucke, J.
%A Vasileiou, V.
%A Vianello, G.
%A Vitale, V.
%A P. Waite, A.
%A Wang, P.
%A L. Winer, B.
%A S. Wood, K.
%A Yang, Z.
%A Zimmer, S.
%< avec comité de lecture
%@ 0004-637X
%J The Astrophysical Journal
%I American Astronomical Society
%V 756
%P 4
%8 2012
%D 2012
%Z 1207.0616
%R 10.1088/0004-637X/756/1/4
%K gamma rays: ISM
%K ISM: clouds
%K ISM: general
%K ISM: individual objects (Orion A and Orion B) Online-only material: color figures
%Z Physics [physics]/Astrophysics [astro-ph]/High Energy Astrophysical Phenomena [astro-ph.HE]
%Z Sciences of the Universe [physics]/Astrophysics [astro-ph]/High Energy Astrophysical Phenomena [astro-ph.HE]Journal articles
%X We report on the gamma-ray observations of giant molecular clouds Orion A and B with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. The gamma-ray emission in the energy band between ∼100 MeV and ∼100 GeV is predicted to trace the gas mass distribution in the clouds through nuclear interactions between the Galactic cosmic rays (CRs) and interstellar gas. The gamma-ray production cross-section for the nuclear interaction is known to ∼10% precision which makes the LAT a powerful tool to measure the gas mass column density distribution of molecular clouds for a known CR intensity. We present here such distributions for Orion A and B, and correlate them with those of the velocity-integrated CO intensity (WCO) at a 1◦ × 1◦ pixel level. The correlation is found to be linear over a WCO range of ∼10-fold when divided in three regions, suggesting penetration of nuclear CRs to most of the cloud volumes. The WCO-to-mass conversion factor, XCO, is found to be ∼2.3 × 1020 cm−2 (K km s−1)−1 for the high-longitude part of Orion A (l > 212◦), ∼1.7 times higher than ∼1.3 × 1020 found for the rest of Orion A and B. We interpret the apparent high XCO in the high-longitude region of Orion A in the light of recent works proposing a nonlinear relation between H2 and CO densities in the diffuse molecular gas. WCO decreases faster than the H2 column density in the region making the gas "darker" to WCO.
%G English
%L in2p3-00747339
%U https://hal.in2p3.fr/in2p3-00747339
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