Ackermann M, Ajello M, Albert A, Atwood WB, Baldini L, Ballet J, Barbiellini G, Bastieri D, Bechtol K, Bellazzini R, Bissaldi E, Blandford RD, Bloom ED, Bottacini E, Brandt TJ, Bregeon J, Bruel P, Buehler R, Buson S, Caliandro GA, Cameron RA, Caragiulo M, Caraveo PA, Cavazzuti E, Cecchi C, Charles E, Chekhtman A, Chiang J, Chiaro G, Ciprini S, Claus R, Cohen-Tanugi J, Conrad J, Cuoco A, Cutini S, D'Ammando F, De Angelis A, De Palma F, Dermer CD, Digel SW, Do Couto E Silva E, Drell PS, Favuzzi C, Ferrara EC, Focke WB, Franckowiak A, Fukazawa Y, Funk S, Fusco P, Gargano F, Gasparrini D, Germani S, Giglietto N, Giommi P, Giordano F, Giroletti M, Godfrey G, Gomez-Vargas GA, Grenier IA, Guiriec S, Gustafsson M, Hadasch D, Hayashi K, Hays E, Hewitt JW, Ippoliti P, Jogler T, Johannesson G, Johnson AS, Johnson WN, Kamae T, Kataoka J, Knoedlseder J, Kuss M, Larsson S, Latronico L, Li J, Li L, Longo F, Loparco F, Lott B, Lovellette MN, Lubrano P, Madejski GM, Manfreda A, Massaro F, Mayer M, Mazziotta MN, Mcenery JE, Michelson PF, Mitthumsiri W, Mizuno T, Moiseev AA, Monzani ME, Morselli A, Moskalenko IV, Murgia S, Nemmen R, Nuss E, Ohsugi T, Omodei N, Orlando E, Ormes JF, Paneque D, Panetta JH, Perkins JS, Pesce-Rollins M, Piron F, Pivato G, Porter TA, Raino S, Rando R, Razzano M, Razzaque S, Reimer A, Reimer O, Reposeur T, Ritz S, Romani RW, Sanchez-Conde M, Schaal M, Schulz A, Sgro C, Siskind EJ, Spandre G, Spinelli P, Strong AW, Suson DJ, Takahashi H, Thayer JG, Thayer JB, Tibaldo L, Tinivella M, Torres DF, Tosti G, Troja E, Uchiyama Y, Vianello G, Werner M, Winer BL, Wood KS, Wood M, Zaharijas G, Zimmer S (2015)

Publication Status: Published

Publication Type: Journal article

Publication year: 2015


Publisher: American Astronomical Society

Book Volume: 799

DOI: 10.1088/0004-637X/799/1/86


The gamma-ray sky can be decomposed into individually detected sources, diffuse emission attributed to the interactions of Galactic cosmic rays with gas and radiation fields, and a residual all-sky emission component commonly called the isotropic diffuse gamma-ray background (IGRB). The IGRB comprises all extragalactic emissions too faint or too diffuse to be resolved in a given survey, as well as any residual Galactic foregrounds that are approximately isotropic. The first IGRB measurement with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi) used 10 months of sky-survey data and considered an energy range between 200 MeV and 100 GeV. Improvements in event selection and characterization of cosmic-ray backgrounds, better understanding of the diffuse Galactic emission (DGE), and a longer data accumulation of 50 months allow for a refinement and extension of the IGRB measurement with the LAT, now covering the energy range from 100 MeV to 820 GeV. The IGRB spectrum shows a significant high-energy cutoff feature and can be well described over nearly four decades in energy by a power law with exponential cutoff having a spectral index of 2.32 +/- 0.02 and a break energy of (279 +/- 52) GeV using our baseline DGE model. The total intensity attributed to the IGRB is (7.2 +/- 0.6) x 10(-6) cm(-2) s(-1) sr(-1) above 100 MeV, with an additional +15%/-30% systematic uncertainty due to the Galactic diffuse foregrounds.

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Involved external institutions

National Institute for Astrophysics / Istituto Nazionale Astrofisica (INAF) IT Italy (IT) Italian Space Agency / Agenzia Spaziale Italiana (ASI) IT Italy (IT) Clemson University US United States (USA) (US) Stanford University US United States (USA) (US) National Institute for Nuclear Physics / Istituto Nazionale di Fisica Nucleare (INFN) IT Italy (IT) University of Chicago US United States (USA) (US) University of California Santa Cruz US United States (USA) (US) University of Montpellier / Université Montpellier FR France (FR) AlbaNova University Centre / Kungliga Tekniska Högskolan AlbaNova Universitetscentrum SE Sweden (SE) Université libre de Bruxelles (ULB) / Free University of Brussels BE Belgium (BE) Japan Aerospace eXploration Agency (JAXA) JP Japan (JP) University of Maryland, Baltimore County (UMBC) US United States (USA) (US) Spanish National Research Council / Consejo Superior de Investigaciones Científicas (CSIC) ES Spain (ES) National Aeronautics and Space Administration (NASA) US United States (USA) (US) Université Bordeaux 1, Sciences et Technologies FR France (FR) Leopold-Franzens-Universität Innsbruck / University of Innsbruck AT Austria (AT) Hiroshima University / 広島大学 JP Japan (JP) Yale University US United States (USA) (US) Mahidol University / มหาวิทยาลัยมหิดล TH Thailand (TH) University of California Irvine US United States (USA) (US) National Academy of Sciences US United States (USA) (US) Stockholm University / Stockholms universitet SE Sweden (SE) University of Johannesburg ZA South Africa (ZA) Ohio State University US United States (USA) (US) Max-Planck-Institut für extraterrestrische Physik (MPE) / Max Planck Institute for Extraterrestrial Physics DE Germany (DE) National Center for Scientific Research / Centre national de la recherche scientifique (CNRS) FR France (FR) Waseda University / 早稲田大学 JP Japan (JP) U.S. Naval Research Laboratory US United States (USA) (US) University of Udine / Università degli Studi di Udine IT Italy (IT) Deutsches Elektronen-Synchrotron DESY DE Germany (DE) University of Paris 7 - Denis Diderot / Université Paris VII Denis Diderot FR France (FR) University of Iceland (UI) / Háskóli Íslands IS Iceland (IS) University of Padua / Universita degli Studi di Padova IT Italy (IT) École Polytechnique - Université Paris-Saclay FR France (FR) University of Maryland US United States (USA) (US) University of Denver US United States (USA) (US) NYCB Real-Time Computing, Inc. US United States (USA) (US) George Mason University US United States (USA) (US)

How to cite


Ackermann, M., Ajello, M., Albert, A., Atwood, W.B., Baldini, L., Ballet, J.,... Zimmer, S. (2015). THE SPECTRUM OF ISOTROPIC DIFFUSE GAMMA-RAY EMISSION BETWEEN 100 MeV AND 820 GeV. Astrophysical Journal, 799.


Ackermann, M., et al. "THE SPECTRUM OF ISOTROPIC DIFFUSE GAMMA-RAY EMISSION BETWEEN 100 MeV AND 820 GeV." Astrophysical Journal 799 (2015).

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