The intermediate-frequency peaked BL Lacertae (IBL) object 3C66A is detected during 2007-2008 in VHE (very high energy; E > 100 GeV) γ rays with the VERITAS stereoscopic array of imaging atmospheric Cherenkov telescopes. An excess of 1791 events is detected, corresponding to a significance of 21.2 standard deviations (σ), in these observations (32.8 hr live time). The observed integral flux above 200 GeV is 6% of the Crab Nebula's flux and shows evidence for variability on the timescale of days. The measured energy spectrum is characterized by a soft power law with photon index Γ = 4.1 0.4stat 0.6sys. The radio galaxy 3C66B is excluded as a possible source of the VHE emission.
Bibliographical noteFunding Information:
This research was supported by grants from the U.S. Department of Energy, the U.S. National Science Foundation and the Smithsonian Institution, by NSERC in Canada, by Science Foundation Ireland, and by STFC in the UK.
- BL Lacertae objects: individual (3C 66A)
- Galaxies: active
- Gamma rays: observations