The Dark Knight Falters

TL;DR

This study challenges the dark matter interpretation of 111 and 129 GeV line emissions by showing most sources are likely active galactic nuclei, suggesting astrophysical processes or instrumental effects as alternative explanations.

Contribution

It applies machine learning and multiwavelength data to identify the nature of line-emitting sources, expanding the possible explanations for the observed gamma-ray features.

Findings

14 of 16 sources are likely AGN

Line features may be due to astrophysical activity in AGN

Alternative explanations include instrumental artifacts or background effects

Abstract

Potential line emission at 111 and 129 GeV from 16 unassociated Fermi-LAT point sources has been reported recently by Su & Finkbeiner (2012c). Together with similar features seen by Fermi in a region near the Galactic Centre, the evidence has been interpreted as the spectral signature of dark matter annihilation or internal bremsstrahlung. Through a combination of supervised machine-learning algorithms and archival multiwavelength observations we find that 14 out of the 16 unassociated sources showing the line emission in the Su & Finkbeiner sample are most likely active galactic nuclei (AGN). Based on this new evidence, one must widen the range of possible solutions for the 100-140 GeV excess to include a very distinct astrophysical explanation. While we cannot rule out a dark matter origin for the line emission in the Galactic Centre, we posit that if the detection in the Su & Finkbeiner sample is indeed real it might be related to accretion, bubble, or jet activity in nearby (z < 0.2) AGN. Alternatively, given the right conditions, the similarity could be due to a chance occurrence caused by extragalactic background light (EBL) absorption. Or else one must concede that the features are an artefact of instrumental or calibration issues.