Where are the Fermi Lines Coming From?

TL;DR

This paper estimates the spatial origins of 110 and 130 GeV gamma-ray features observed by Fermi-LAT, assessing their consistency with dark matter annihilation sources at the galactic center using advanced localization and background modeling techniques.

Contribution

It introduces a data-driven background model and per-photon incident angle analysis to localize gamma-ray features and evaluate their association with a central dark matter halo.

Findings

The 130 GeV line is offset from the galactic center by about 280 pc.

The 110 GeV line is offset by about 30-60 pc.

Displacements are consistent with a central dark matter halo at statistical significance.

Abstract

We estimate the spatial locations of sources of the the observed features in the Fermi-LAT photon spectrum at $E_\gamma=110$ and $E_\gamma=130$ GeV. We determine whether they are consistent with emission from a single source, as would be expected in their interpretation as $\gamma\gamma$ and $\gamma Z$ lines from dark matter annhiliation, as well as whether they are consistent with a dark matter halo positioned at the center of the galaxy. We take advantage of the per-photon measured incident angle in reconstructing the line features. In addition, we use a data-driven background model rather than making the assumption of a feature-less background. We localize the sources of the features at 110 and 130 GeV. Assuming an Einasto (NFW) density model we find the 130 GeV line to be offset from the galactic center by 285 (280) pc, the 110 GeV line by 60 (30) pc with a large relative separation of 220 (240) pc. However, we find this displacement of each source from the galactic center, as well as their relative displacement to be statistically consistent with a single Einasto or NFW dark matter halo at the center of the galaxy.