CONSTRAINTS ON THE COSMIC-RAY DENSITY GRADIENT BEYOND THE SOLAR CIRCLE FROM FERMI gamma-RAY OBSERVATIONS OF THE THIRD GALACTIC QUADRANT

Ackermann M, Ajello M, Baldini L, Ballet J, Barbiellini G, Bastieri D, Bechtol K, Bellazzini R, Berenji B, Bloom ED, Bonamente E, Borgland AW, Brandt TJ, Bregeon J, Brez A, Brigida M, Bruel P, Buehler R, Buson S, Caliandro GA, Cameron RA, Caraveo PA, Casandjian JM, Cecchi C, Charles E, Chekhtman A, Chiang J, Ciprini S, Claus R, Cohen-Tanugi J, Conrad J, Dermer CD, De Palma F, Digel SW, Drell PS, Dubois R, Favuzzi C, Ferrara EC, Focke WB, Fukazawa Y, Funk S, Fusco P, Gargano F, Germani S, Giglietto N, Giordano F, Giroletti M, Glanzman T, Godfrey G, Grenier IA, Guiriec S, Hadasch D, Hanabata Y, Harding AK, Hayashi K, Hayashida M, Hughes RE, Itoh R, Johannesson G, Johnson AS, Johnson WN, Kamae T, Katagiri H, Kataoka J, Knoedlseder J, Kuss MW, Lande J, Latronico L, Lee SH, Garde ML, Longo F, Loparco F, Lovellette MN, Lubrano P, Makeev A, Martin P, Mazziotta MN, Mcenery JE, Mehault J, Michelson PF, Mizuno T, Monte C, Monzani ME, Morselli A, Moskalenko IV, Murgia S, Naumann-Godo M, Nishino S, Nolan PL, Norris JP, Nuss E, Ohsugi T, Okumura A, Omodei N, Orlando E, Ormes JF, Ozaki M, Parent D, Pelassa V, Pepe M, Pesce-Rollins M, Piron F, Porter TA, Raino S, Rando R, Razzano M, Reimer A, Reimer O, Ripken J, Sada T, Sadrozinski HFW, Sgro C, Siskind EJ, Spandre G, Spinelli P, Strickman MS, Strong AW, Suson DJ, Takahashi HH, Takahashi T, Tanaka T, Thayer JB, Thompson DJ, Tibaldo L, Torres DF, Tramacere A, Uchiyama Y, Uehara T, Usher TL, Vandenbroucke J, Vasileiou V, Vilchez N, Vitale V, Vladimirov AE, Waite AP, Wang P, Wood KS, Yang Z, Ziegler M (2011)

Publication Type: Journal article

Publication year: 2011

Journal

Book Volume: 726

Journal Issue: 2

DOI: 10.1088/0004-637X/726/2/81

Abstract

We report an analysis of the interstellar gamma-ray emission in the third Galactic quadrant measured by the Fermi Large Area Telescope. The window encompassing the Galactic plane from longitude 210 degrees to 250 degrees has kinematically well-defined segments of the Local and the Perseus arms, suitable to study the cosmic-ray (CR) densities across the outer Galaxy. We measure no large gradient with Galactocentric distance of the gamma-ray emissivities per interstellar H atom over the regions sampled in this study. The gradient depends, however, on the optical depth correction applied to derive the H I column densities. No significant variations are found in the interstellar spectra in the outer Galaxy, indicating similar shapes of the CR spectrum up to the Perseus arm for particles with GeV to tens of GeV energies. The emissivity as a function of Galactocentric radius does not show a large enhancement in the spiral arms with respect to the interarm region. The measured emissivity gradient is flatter than expectations based on a CR propagation model using the radial distribution of supernova remnants and uniform diffusion properties. In this context, observations require a larger halo size and/or a flatter CR source distribution than usually assumed. The molecular mass calibrating ratio, X-CO = N(H-2)/W-CO, is found to be (2.08 +/- 0.11) x 10(20) cm(-2)(K km s(-1))(-1) in the Local arm clouds and is not significantly sensitive to the choice of Hi spin temperature. No significant variations are found for clouds in the interarm region.

Authors with CRIS profile

Involved external institutions

Stanford University United States (USA) (US) National Institute for Nuclear Physics / Istituto Nazionale di Fisica Nucleare (INFN) Italy (IT) University of Paris 7 - Denis Diderot / Université Paris VII Denis Diderot France (FR) Université Toulouse III - Paul Sabatier France (FR) University of Bari Aldo Moro / Università degli Studi di Bari Aldo Moro Italy (IT) École Polytechnique - Université Paris-Saclay France (FR) Spanish National Research Council / Consejo Superior de Investigaciones Científicas (CSIC) Spain (ES) National Institute for Astrophysics / Istituto Nazionale Astrofisica (INAF) Italy (IT) U.S. Naval Research Laboratory United States (USA) (US) Università degli Studi di Perugia Italy (IT) University of Montpellier / Université Montpellier France (FR) Stockholm University / Stockholms universitet Sweden (SE) National Aeronautics and Space Administration (NASA) United States (USA) (US) Hiroshima University / 広島大学 Japan (JP) University of Alabama in Huntsville (UAH) United States (USA) (US) Ohio State University United States (USA) (US) Waseda University / 早稲田大学 Japan (JP) Max-Planck-Institut für extraterrestrische Physik (MPE) / Max Planck Institute for Extraterrestrial Physics Germany (DE) University of Denver United States (USA) (US) Japan Aerospace eXploration Agency (JAXA) Japan (JP) University of California Santa Cruz United States (USA) (US) NYCB Real-Time Computing, Inc. United States (USA) (US) Purdue University Northwest / Purdue University Calumet United States (USA) (US) Institut d'Estudis Espacials de Catalunya (IEEC) Spain (ES)

How to cite

APA:

Ackermann, M., Ajello, M., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D.,... Ziegler, M. (2011). CONSTRAINTS ON THE COSMIC-RAY DENSITY GRADIENT BEYOND THE SOLAR CIRCLE FROM FERMI gamma-RAY OBSERVATIONS OF THE THIRD GALACTIC QUADRANT. Astrophysical Journal, 726(2). https://doi.org/10.1088/0004-637X/726/2/81

MLA:

Ackermann, Markus, et al. "CONSTRAINTS ON THE COSMIC-RAY DENSITY GRADIENT BEYOND THE SOLAR CIRCLE FROM FERMI gamma-RAY OBSERVATIONS OF THE THIRD GALACTIC QUADRANT." Astrophysical Journal 726.2 (2011).

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