title: Discovery of a new population of high-energy gamma-ray sources in the Milky Way
abstract: One of the great mysteries of the high-energy gamma-ray sky is the group of approximately 170 unidentified point sources found along the Galactic plane. They are more numerous than all other high-energy gamma-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 approximately 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 belt of massive stars and gas clouds at approximately 600 light years distance, as has been previously suggested.
authors.affiliation: Laboratory for High Energy Astrophysics, NASA's Goddard Space Flight Centre, Greenbelt, Maryland 20771, USA. gehrels@gsfc.nasa.gov
authors.initials: N
authors.lastname: Gehrels
authors.initials: DJ
authors.lastname: Macomb
authors.initials: DL
authors.lastname: Bertsch
authors.initials: DJ
authors.lastname: Thompson
authors.initials: RC
authors.lastname: Hartman