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N. Gehrels, D. J. Macomb, D. L. Bertsch, D. J. Thompson, R. C. Hartman (NASA GSFC)
One of the great mysteries of the high energy gamma-ray sky is the existence of a large number of unidentified point sources. They account for more than half of the sources detected by the EGRET instrument on CGRO, numbering 171 out of 270 total sources in the recent 3rd EGRET catalog. No clear counterparts have been found at other wavelengths despite 20 years of effort. In this presentation, we will show evidence for a new population of these sources in the 3rd EGRET catalog. A cluster of ~20 faint sources appears concentrated near the galactic center, extending to ~30° galactic latitude and with more sources toward positive latitudes than negative. They are part of a broader class of faint sources sprinkled around the sky at mid-latitudes. Several tests show that they are real point sources and that they are distinct from the population of bright unidentified sources that lie along the galactic plane. The distribution on the sky indicates that the faint mid-latitude sources are local in origin (~100 pc distant) and may be associated with the Gould Belt. Candidates for the counterparts of these sources include massive stars (gamma rays generated in the stellar wind), radio quiet gamma-ray pulsars and jets from accreting black holes.
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