Investigating the uniformity of the excess gamma rays towards the galactic center region

We perform a composite likelihood analysis of subdivided regions within the central 26 degrees x20 degrees of the MilkyWay, with the aim of characterizing the spectrum of the gamma-ray galactic center excess in regions of varying galactocentric distance. Outside of the innermost few degrees, we fi nd that the radial pro fi le of the excess is background-model dependent and poorly constrained. The spectrum of the excess emission is observed to extend upwards of 10 GeV outside similar to 5 degrees ffi in radius, but cuts o ff steeply between 10-20 GeV only in the innermost few degrees. If interpreted as a real feature of the excess, this radial variation in the spectrum has important implications for both astrophysical and dark matter interpretations of the galactic center excess. Single-component dark matter annihilation models face challenges in reproducing this variation; on the other hand, a population of unresolved millisecond pulsars contributing both prompt and secondary inverse Compton emission may be able to explain the spectrum as well as its spatial dependency. We show that the expected di ff erences in the photon-count distributions of a smooth dark matter annihilation signal and an unresolved point source population are an order of magnitude smaller than the fluctuations in residuals after fi tting the data, which implies that mismodeling is an important systematic e ff ect in point source analyses aimed at resolving the gamma-ray excess.