Discovery of a new population of high-energy γ-ray sources in the Milky Way

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Abstract
One of the great mysteries of the high-energy γ-ray sky is the group of ∼170 unidentified point sources1,2 found along the Galactic plane. They are more numerous than all other high-energy γ-ray sources combined and, despite 20 years of effort, no clear counterparts have been found at other wavelengths. Here we report a new population of such objects. A cluster of ∼20 faint sources appears north of the Galactic Centre, which is part of a broader class of faint objects at mid-latitudes. In addition, we show in a model-independent way that the mid-latitude sources are distinct from the population of bright unidentified sources along the Galactic plane. The distribution on the sky indicates that the faint mid-latitude sources are associated with the Gould belt3,4 of massive stars and gas clouds at ∼600 light years distance, as has been previously suggested5.