The angular power spectrum of the diffuse gamma-ray emission as measured
  by the Fermi Large Area Telescope and constraints on its Dark Matter
  interpretation
  The isotropic gamma-ray background arises from the contribution of unresolved
sources, including members of confirmed source classes and proposed gamma-ray
emitters such as the radiation induced by dark matter annihilation and decay.
Clues about the properties of the contributing sources are imprinted in the
anisotropy characteristics of the gamma-ray background. We use 81 months of
Pass 7 Reprocessed data from the Fermi Large Area Telescope to perform a
measurement of the anisotropy angular power spectrum of the gamma-ray
background. We analyze energies between 0.5 and 500 GeV, extending the range
considered in the previous measurement based on 22 months of data. We also
compute, for the first time, the cross-correlation angular power spectrum
between different energy bins. We find that the derived angular spectra are
compatible with being Poissonian, i.e. constant in multipole. Moreover, the
energy dependence of the anisotropy suggests that the signal is due to two
populations of sources, contributing, respectively, below and above 2 GeV.
Finally, using data from state-of-the-art numerical simulations to model the
dark matter distribution, we constrain the contribution from dark matter
annihilation and decay in Galactic and extragalactic structures to the measured
anisotropy. These constraints are competitive with those that can be derived
from the average intensity of the isotropic gamma-ray background. Data are
available at https://www-glast.stanford.edu/pub_data/552.
