The dark knight falters

Abstract

Abstract Tentative line emission at 111 and 129 GeV from 16 unassociated Fermi-LAT point sources has been reported recently by Su and Finkbeiner. 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 that the line emission in the Su and 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 and 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 absorption. Or else one must concede that the features are an artefact of instrumental or calibration issues.