Foreground Mismodeling and the Point Source Explanation of the Fermi
  Galactic Center Excess
  The Fermi Large Area Telescope has observed an excess of ~GeV energy gamma
rays from the center of the Milky Way, which may arise from near-thermal dark
matter annihilation. Firmly establishing the dark matter origin for this excess
is however complicated by challenges in modeling diffuse cosmic-ray foregrounds
as well as unresolved astrophysical sources, such as millisecond pulsars.
Non-Poissonian Template Fitting (NPTF) is one statistical technique that has
previously been used to show that at least some fraction of the GeV excess is
likely due to a population of dim point sources. These results were recently
called into question by Leane and Slatyer (2019), who showed that a synthetic
dark matter annihilation signal injected on top of the real Fermi data is not
recovered by the NPTF procedure. In this work, we perform a dedicated study of
the Fermi data and explicitly show that the central result of Leane and Slatyer
(2019) is likely driven by the fact that their choice of model for the Galactic
foreground emission does not provide a sufficiently good description of the
data. We repeat the NPTF analyses using a state-of-the-art model for diffuse
gamma-ray emission in the Milky Way and introduce a novel statistical
procedure, based on spherical-harmonic marginalization, to provide an improved
description of the Galactic diffuse emission in a data-driven fashion. With
these improvements, we find that the NPTF results continue to robustly favor
the interpretation that the Galactic Center excess is due, in part, to
unresolved astrophysical point sources across the analysis variations that we
have explored.
