Many independent groups have claimed to find an unaccounted excess
over conventional diffuse backgrounds in the data collected by the
Fermi-LAT from the Galactic Center. The excess is compatible with dark
matter predictions, nevertheless the modelling of gamma-ray sources in
the line of sight of the Milky Way’s center is full of uncertainties.
I will present preliminary results of a Fermi-LAT Collaboration
analysis of the diffuse emission toward to the Galactic Center that
give important insight on the excess nature. Different phenomena could
account for the Galactic Center excess in gamma rays. Besides the dark
matter interpretation, the other phenomena that may account for the
excess are: a population of yet unresolved millisecond pulsars located
in the bulge of the Milky Way, and secondary emission from cosmic-ray
protons or electrons injected in the Galactic Center by past events.
To distinguish between an unresolved population of point sources and
an intrinsic diffuse emission as the real nature of the Galactic
Center excess is challenging. I will present some statistical methods
proposed to shed light on this issue, in particular the 1pt-PDF
(number of pixels with k counts vs k counts) to characterize the
clustering properties.