The Spatial Morphology of the Secondary Emission in the Galactic Center Gamma-Ray Excess

TL;DR

This paper investigates the role of secondary electron and positron emission in explaining the Galactic Center gamma-ray excess, developing a method to assess their spatial morphology and importance in modeling the observed data.

Contribution

It introduces a novel approach to test the significance of secondary emission in gamma-ray excess models considering their spatial distribution.

Findings

Secondary emission can significantly impact gamma-ray excess modeling.

Broadband analysis alone may be insufficient to identify secondary emission contributions.

A new method for assessing the importance of secondary emission based on spatial morphology is proposed.

Abstract

Excess GeV gamma rays from the Galactic Center (GC) have been measured with the Fermi Large Area Telescope (LAT). The presence of the GC excess (GCE) appears to be robust with respect to changes in the diffuse galactic background modeling. The three main proposals for the GCE are an unresolved population of millisecond pulsars (MSPs), outbursts of cosmic rays from the GC region, and self-annihilating dark matter (DM). The injection of secondary electrons and positrons into the interstellar medium (ISM) by an unresolved population of MSPs or DM annihilations can lead to observable gamma-ray emission via inverse Compton scattering or bremsstrahlung. Here we investigate how to determine whether secondaries are important in a model for the GCE. We develop a method of testing model fit which accounts for the different spatial morphologies of the secondary emission. We examine several models which give secondary emission and illustrate a case where a broadband analysis is not sufficient to determine the need for secondary emission.