GAMMA-RAY OBSERVATIONS OF THE ORION MOLECULAR CLOUDS WITH THE FERMI LARGE AREA TELESCOPE

Ackermann, M.; Ajello, M.; Allafort, A.; Antolini, E.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, Denis; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bottacini, EUGENIO ALESSIO; Brandt, T. J.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, Sara; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Cecchi, C.; Chekhtman, A.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen Tanugi, J.; Conrad, J.; D'Ammando, F.; de Angelis, A.; de Palma, F.; Dermer, C. D.; Silva, E. do Couto e.; Drell, P. S.; Drlica Wagner, A.; Enoto, T.; Falletti, L.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fukazawa, Y.; Fukui, Y.; Fusco, P.; Gargano, F.; Gasparrini, D.; Germani, S.; Giglietto, N.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Guiriec, S.; Hadasch, D.; Hanabata, Y.; Harding, A. K.; Hayashida, M.; Hayashi, K.; Horan, D.; Hou, X.; Hughes, R. E.; Jackson, M. S.; Jóhannesson, G.; Johnson, A. S.; Kamae, T.; Katagiri, H.; Kataoka, J.; Kerr, M.; Knödlseder, J.; Kuss, M.; Lande, J.; Larsson, S.; Lee, S. H.; Longo, F.; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Makishima, K.; Mazziotta, M. N.; Mehault, J.; Mitthumsiri, W.; Moiseev, A. A.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nakamori, T.; Naumann Godo, M.; Nishino, S.; Norris, J. P.; Nuss, E.; Ohno, M.; Ohsugi, T.; Okumura, A.; Orienti, M.; Orlando, E.; Ormes, J. F.; Ozaki, M.; Paneque, D.; Panetta, J. H.; Parent, D.; Pelassa, V.; Pesce Rollins, M.; Pierbattista, M.; Piron, F.; Pivato, Giovanna; Porter, T. A.; Rainò, S.; Razzano, M.; Reimer, A.; Reimer, O.; Roth, M.; Sadrozinski, H. F. W.; Sgrò, C.; Siskind, E. J.; Spandre, G.; Spinelli, P.; Strong, A. W.; Takahashi, H.; Takahashi, T.; Tanaka, T.; Thayer, J. G.; Thayer, J. B.; Tibolla, O.; Tinivella, M.; Torres, D. F.; Tramacere, A.; Troja, E.; Uchiyama, Y.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vianello, G.; Vitale, V.; Waite, A. P.; Wang, P.; Winer, B. L.; Wood, K. S.; Yang, Z.; Zimmer, S.

doi:10.1088/0004-637X/756/1/4

Padua Research Archive, l’archivio istituzionale della produzione scientifica dell’Università degli Studi di Padova, ha lo scopo di raccogliere, documentare, conservare e pubblicare, anche ad accesso aperto, i prodotti della ricerca dell’Ateneo. Padua Research Archive utilizza la piattaforma IRIS (Institutional Research Information System) sviluppata da Cineca.

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 (W CO) at a 1° × 1° pixel level. The correlation is found to be linear over a W CO range of ~10-fold when divided in three regions, suggesting penetration of nuclear CRs to most of the cloud volumes. The W CO-to-mass conversion factor, X CO, 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 X CO 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. W CO decreases faster than the H2 column density in the region making the gas "darker" to W CO.

Titolo:	GAMMA-RAY OBSERVATIONS OF THE ORION MOLECULAR CLOUDS WITH THE FERMI LARGE AREA TELESCOPE
Autori:	M. Ackermann M. Ajello A. Allafort E. Antolini L. Baldini J. Ballet G. Barbiellini BASTIERI, DENIS K. Bechtol R. Bellazzini B. Berenji R. D. Blandford E. D. Bloom E. Bonamente A. W. Borgland BOTTACINI, EUGENIO ALESSIO T. J. Brandt J. Bregeon M. Brigida P. Bruel R. Buehler BUSON, SARA G. A. Caliandro R. A. Cameron P. A. Caraveo C. Cecchi A. Chekhtman J. Chiang S. Ciprini R. Claus J. Cohen Tanugi J. Conrad F. D'Ammando A. de Angelis F. de Palma C. D. Dermer E. do Couto e. Silva P. S. Drell A. Drlica Wagner T. Enoto L. Falletti C. Favuzzi S. J. Fegan E. C. Ferrara W. B. Focke Y. Fukazawa Y. Fukui P. Fusco F. Gargano D. Gasparrini S. Germani N. Giglietto F. Giordano M. Giroletti T. Glanzman G. Godfrey S. Guiriec D. Hadasch Y. Hanabata A. K. Harding M. Hayashida K. Hayashi D. Horan X. Hou R. E. Hughes M. S. Jackson G. Jóhannesson A. S. Johnson T. Kamae H. Katagiri J. Kataoka M. Kerr J. Knödlseder M. Kuss J. Lande S. Larsson S. H. Lee F. Longo F. Loparco M. N. Lovellette P. Lubrano K. Makishima M. N. Mazziotta J. Mehault W. Mitthumsiri A. A. Moiseev C. Monte M. E. Monzani A. Morselli I. V. Moskalenko S. Murgia T. Nakamori M. Naumann Godo S. Nishino J. P. Norris E. Nuss M. Ohno T. Ohsugi A. Okumura M. Orienti E. Orlando J. F. Ormes M. Ozaki D. Paneque J. H. Panetta D. Parent V. Pelassa M. Pesce Rollins M. Pierbattista F. Piron PIVATO, GIOVANNA T. A. Porter S. Rainò M. Razzano A. Reimer O. Reimer M. Roth H. F. W. Sadrozinski C. Sgrò E. J. Siskind G. Spandre P. Spinelli A. W. Strong H. Takahashi T. Takahashi T. Tanaka J. G. Thayer J. B. Thayer O. Tibolla M. Tinivella D. F. Torres A. Tramacere E. Troja Y. Uchiyama T. L. Usher J. Vandenbroucke V. Vasileiou G. Vianello V. Vitale A. P. Waite P. Wang B. L. Winer K. S. Wood Z. Yang S. Zimmer mostra contributor esterni nascondi contributor esterni
Data di pubblicazione:	2012
Rivista:	THE ASTROPHYSICAL JOURNAL
Abstract:	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 (W CO) at a 1° × 1° pixel level. The correlation is found to be linear over a W CO range of ~10-fold when divided in three regions, suggesting penetration of nuclear CRs to most of the cloud volumes. The W CO-to-mass conversion factor, X CO, 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 X CO 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. W CO decreases faster than the H2 column density in the region making the gas "darker" to W CO.
Handle:	http://hdl.handle.net/11577/2828987
Appare nelle tipologie:	01.01 - Articolo in rivista

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