Letters to Nature
Nature 404, 363-365 (23 March 2000) | doi:10.1038/35006001; Received 8 October 1999; Accepted 5 January 2000
Discovery of a new population of high-energy 
-ray sources in the
Milky Way
N. Gehrels, D. J. Macomb, D. L. Bertsch, D. J. Thompson & R. C. Hartman
- Laboratory for High Energy Astrophysics, NASA's Goddard Space Flight Centre, Greenbelt, Maryland 20771, USA
Correspondence to: N. Gehrels Correspondence and requests for materials should be addressed to N. G. (e-mail: Email: gehrels@gsfc.nasa.gov).
One of the great mysteries of the high-energy 
-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 -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.
