Dark Matter and Pulsar Model Constraints from Galactic Center Fermi-LAT
  Gamma Ray Observations
  Employing Fermi-LAT gamma ray observations, several independent groups have
found excess extended gamma ray emission at the Galactic center (GC). Both,
annihilating dark matter (DM) or a population of $\sim 10^3$ unresolved
millisecond pulsars (MSPs) are regarded as well motivated possible
explanations. However, there is significant uncertainties in the diffuse
galactic background at the GC. We have performed a revaluation of these two
models for the extended gamma ray source at the GC by accounting for the
systematic uncertainties of the Galactic diffuse emission model. We also
marginalize over point source and diffuse background parameters in the region
of interest. We show that the excess emission is significantly more extended
than a point source. We find that the DM (or pulsars population) signal is
larger than the systematic errors and therefore proceed to determine the
sectors of parameter space that provide an acceptable fit to the data. We found
that a population of order a 1000 MSPs with parameters consistent with the
average spectral shape of Fermi-LAT measured MSPs was able to fit the GC excess
emission. For DM, we found that a pure $\tau^+\tau^-$ annihilation channel is
not a good fit to the data. But a mixture of $\tau^+\tau^-$ and $b\bar{b}$ with
a $\left<\sigma v\right>$ of order the thermal relic value and a DM mass of
around 20 to 60 GeV provides an adequate fit.
