The Gamma-Ray Pulsar Population of Globular Clusters: Implications for
  the GeV Excess
  It has been suggested that the GeV excess, observed from the region
surrounding the Galactic Center, might originate from a population of
millisecond pulsars that formed in globular clusters. With this in mind, we
employ the publicly available Fermi data to study the gamma-ray emission from
157 globular clusters, identifying a statistically significant signal from 25
of these sources (ten of which are not found in existing gamma-ray catalogs).
We combine these observations with the predicted pulsar formation rate based on
the stellar encounter rate of each globular cluster to constrain the gamma-ray
luminosity function of millisecond pulsars in the Milky Way's globular cluster
system. We find that this pulsar population exhibits a luminosity function that
is quite similar to those millisecond pulsars observed in the field of the
Milky Way (i.e. the thick disk). After pulsars are expelled from a globular
cluster, however, they continue to lose rotational kinetic energy and become
less luminous, causing their luminosity function to depart from the
steady-state distribution. Using this luminosity function and a model for the
globular cluster disruption rate, we show that millisecond pulsars born in
globular clusters can account for only a few percent or less of the observed
GeV excess. Among other challenges, scenarios in which the entire GeV excess is
generated from such pulsars are in conflict with the observed mass of the Milky
Way's Central Stellar Cluster.
