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  • The \(\gamma\)-ray Milky Way above 10 GeV:
    Distinguishing Sources from Diffuse Emission

    Abstract

    One of the most prominent features of the gamma-ray sky is the emission from our own galaxy. The Galactic plane has been observed by Fermi/LAT in GeV and H.E.S.S. in TeV light. Fermi has modeled the Galactic emission as the sum of a complex “diffuse” emission model with the predominately point source catalogs of 1FHL and 2FGL, while H.E.S.S. has primarily detected extended TeV sources. At GeV energies, Galactic diffuse emission dominates the gamma-ray Milky Way but, as sources have hard spectra, it is likely their emission dominates at TeV energies. Generally the spatial shape and fraction of source emission compared to diffuse emission in the Galactic plane is not well known and is dependent on the source detection method, threshold and diffuse emission modeling methods used.
    We present simple image-analysis based methods applied to Fermi data from 10 GeV to 500 GeV, covering a region of +/- 5 degrees in Galactic latitude and +/- 100 degrees in Galactic longitude, to separate source and diffuse emission. These methods include significance clipping to exclude sources combined with elongated filter smoothing and template fitting with Planck and a Gaussian band model. We compare these methods with one another, and also against models based on the Fermi 1FHL catalog, and apply them to very simple model Galaxies to test the response for an input of known fraction and shape of diffuse and source emission.

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