Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The origin of the Fermi-LAT $\gamma$-ray background   The origin of the Isotropic Diffuse $\gamma$-Ray Background (IGRB) is one of
the most intriguing mystery in astrophysics. Recently the Large Area Telescope
(LAT) on board the Fermi Gamma-Ray Space Telescope has measured the IGRB
spectrum from 100 MeV to 820 GeV. Thousands of extragalactic sources are
detected at $\gamma$-ray energies and, thanks to Fermi-LAT catalogs and to
population studies, we show that the IGRB can be explained, in the entire
energy range, by the $\gamma$-ray emission from unresolved misaligned Active
Galactic Nuclei, blazars and Star Forming Galaxies. Finally we derive, with a
dedicated analysis based on the 2FHL Fermi-LAT catalog at $E>50$ GeV, the
intrinsic source count distribution of blazars and demonstrate that this source
population explains the $86^{+16}_{-14}\%$ of the total extragalactic
$\gamma$-ray background.

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The categories of this paper are: cond-mat
35
The categories of this paper are: mtrl-th
11
The categories of this paper are: hep-lat
36
The categories of this paper are: cmp-lg
37
The categories of this paper are: supr-con
12
The categories of this paper are: nucl-th
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The categories of this paper are: math
3
The categories of this paper are: physics
21
The categories of this paper are: adap-org
1
The categories of this paper are: cs
20
The categories of this paper are: acc-phys
13
The categories of this paper are: quant-ph
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The categories of this paper are: funct-an
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The categories of this paper are: stat
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-ex