Inverse-Compton emission from Millisecond Pulsars in the Galactic bulge

Deheng Song, Oscar Macias, Shunsaku Horiuchi

Published 2019-01-21Version 1

Analyses of $\textit{Fermi Gamma-Ray Space Telescope}$ data have revealed a source of excess diffuse gamma rays towards the Galactic center that extends up to roughly $\pm 20$ degrees in latitude. The leading theory postulates that this GeV excess is the aggregate emission from a large number of faint millisecond pulsars (MSPs). The electrons and positrons ($e^{\pm}$) injected by this population could produce detectable inverse-Compton (IC) emissions by up-scattering ambient photons to gamma-ray energies. In this work, we calculate such IC emissions using $\texttt{GALPROP}$. A triaxial 3D model of the bulge stars obtained from a fit to infrared data is used as a tracer of the putative MSP population. This model is compared against one in which the MSPs are spatially distributed as a Navarro-Frenk-White squared profile. We show that the resulting spectra for both models are indistinguishable, but that their spatial morphologies have salient recognizable features. The IC component above $\sim $ TeV energies carry information on the spatial morphology of the injected $e^\pm$. Such differences could potentially be used by future high-energy gamma-ray detectors such as Cherenkov Telescope Array (CTA) to provide a viable multiwavelength handle for the MSP origin of the GeV excess.