M. AckermannM. AjelloA. AlbertW. B. AtwoodL. BaldiniJ. BalletG. BarbielliniD. BastieriK. BechtolR. BellazziniE. BissaldiR. D. BlandfordE. D. BloomE. BottaciniT. J. BrandtJ. BregeonP. BruelR. BuehlerS. BusonG. A. CaliandroR. A. CameronM. CaragiuloP. A. CaraveoE. CavazzutiC. CecchiE. CharlesA. ChekhtmanJ. ChiangG. ChiaroS. CipriniR. ClausJ. Cohen-TanugiJ. ConradA. CuocoS. CutiniF. D'AmmandoA. De AngelisF. De PalmaC. D. DermerS. W. DigelE. Do Couto E SilvaP. S. DrellC. FavuzziE. C. FerraraW. B. FockeA. FranckowiakY. FukazawaS. FunkP. FuscoF. GarganoD. GasparriniS. GermaniN. GigliettoP. GiommiF. GiordanoM. GirolettiG. GodfreyG. A. Gomez-VargasI. A. GrenierS. GuiriecM. GustafssonD. HadaschK. HayashiE. HaysJ. W. HewittP. IppolitiT. JoglerG. JóhannessonA. S. JohnsonW. N. JohnsonT. KamaeJ. KataokaJ. KnödlsederM. KussS. LarssonDeutsche Elektronen-SynchrotronClemson UniversityKavli Institute for Particle Astrophysics and CosmologySanta Cruz Institute for Particle PhysicsIstituto Nazionale di Fisica Nucleare, RomaInstitut de Recherche sur les Lois Fondamentales de l'UniversUniversita degli Studi di TriesteIstituto Nazionale Di Fisica Nucleare, Sezione di PadovaUniversita degli Studi di PadovaUniversity of ChicagoNASA Goddard Space Flight CenterLaboratoire Univers et Particules de MontpellierLaboratoire Leprince-RinguetConsorzio Interuniversitario per la Fisica Spaziale (CIFS)INAF Istituto di Astrofisica Spaziale e Fisica Cosmica, MilanAgenzia Spaziale ItalianaUniversita degli Studi di PerugiaGeorge Mason University, Fairfax CampusOsservatorio Astronomico di RomaStockholms universitetOskar Klein Centre for Cosmoparticle PhysicsKungl. VetenskapsakademienUniversita degli Studi di TorinoIstituto Di Radioastronomia, BolognaAlma Mater Studiorum Universita di BolognaUniversita degli Studi di Napoli Federico IINaval Research LaboratoryUniversita degli Studi di BariHiroshima UniversityPontificia Universidad Catolica de ChileUniversité libre de Bruxelles (ULB)Medizinische Universitat InnsbruckJAXA Institute of Space and Astronautical ScienceUniversity of Maryland, Baltimore CountyUniversity Science Institute ReykjavikWaseda UniversityCNRS Centre National de la Recherche ScientifiqueUniversite de ToulouseInstituto de Estudios Espaciales de CatalunaThe Royal Institute of Technology (KTH)Centre d'Etudes Nucleaires de Bordeaux GradignanYale UniversityUniversity of MarylandMahidol UniversityUniversity of California, Irvine2018-11-232018-11-232015-01-20Astrophysical Journal. Vol.799, No.1 (2015)153843570004637X2-s2.0-84921629099https://repository.li.mahidol.ac.th/handle/20.500.14594/35887© 2015. The American Astronomical Society. All rights reserved. The γ-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 γ-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.Mahidol UniversityEarth and Planetary SciencesArticleSCOPUS10.1088/0004-637X/799/1/86