Characterizing the population of pulsars in the Galactic bulge with the $Fermi$ Large Area Telescope

Fermi-LAT Collaboration

Published 2017-04-28Version 1

An excess of $\gamma$-ray emission from the Galactic Center (GC) region with respect to predictions based on a variety of interstellar emission models and $\gamma$-ray source catalogs has been found by many groups using data from the $Fermi$ Large Area Telescope (LAT). Several interpretations of this excess have been invoked. In this paper we test the interpretation that the excess is caused by an unresolved population of $\gamma$-ray pulsars located in the Galactic bulge. We use cataloged LAT sources to derive criteria that efficiently select pulsars with very small contamination from blazars. We search for point sources in the inner $40^\circ\times40^\circ$ region of the Galaxy, derive a list of approximately 400 sources, and apply pulsar selection criteria to extract pulsar candidates among our source list. We also derive the efficiency of these selection criteria for $\gamma$-ray pulsars as a function of source energy flux and location. We demonstrate that given the observed spatial and flux distribution of pulsar candidates, a model that includes a population with about 2.7 $\gamma$-ray pulsars in the Galactic disk (in our $40^\circ\times40^\circ$ analysis region) for each pulsar in the Galactic bulge is preferred at the level of 7~standard deviations with respect to a disk-only model. The properties of these disk and bulge pulsar populations are consistent with the population of known $\gamma$-ray pulsars as well as with the spatial profile and energy spectrum of the GC excess. Finally, we show that the dark matter interpretation of the GC excess is strongly disfavored since a distribution of dark matter is not able to mimic the observed properties of the population of sources detected in our analysis.