High-Energy Gamma Rays from the BL Lacertae Object PKS 2155-304
Abstract
We present the first detection of gamma-ray emission from the extragalactic source PKS 2155-304, which is often considered to be a prototype of X-ray--selected BL Lacertae objects. The 30 MeV--10 GeV photon spectrum derived from measurements taken with EGRET on the Compton Observatory during 1994 November 15--29 indicates a very hard spectrum with a power-law spectral index of 1.71 +/- 0.24. This spectral hardness when combined with the proximity of the source (z = 0.116) makes it an excellent candidate for detection at TeV gamma-ray energies. We briefly discuss the implications of these gamma-ray measurements for models of BL Lac objects.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 1995
- DOI:
- 10.1086/309790
- Bibcode:
- 1995ApJ...454L..93V
- Keywords:
-
- GAMMA RAYS: OBSERVATIONS;
- GALAXIES: BL LACERTAE OBJECTS: INDIVIDUAL ALPHANUMERIC: PKS 2155-304