A survey of unidentified egret sources at very high energies

The Whipple Observatory 10 m γ-ray telescope has been used to survey the error boxes of EGRET unidentified sources in an attempt to find counterparts at energies of 350 GeV and above. Twenty-one unidentified sources detected by EGRET (more than 10% of the total number) have been included in this survey. In no case is a statistically significant signal found in the EGRET error box, which implies that, at least for this sample, the γ-ray spectra of these sources steepen between 100 Me V and 350 GeV. For each EGRET source location, we list candidate associations and derive upper limits on the integral γ-ray flux above 350 GeV. © 2005. The American Astronomical Society. All rights reserved.