VERITAS Collaboration: V. A. Acciari, et al.
(incl. M. Böttcher),
Astrophysical Journal Letters, 693, L104 (2009)
The intermediate-frequency peaked BL Lacertae (IBL) object 3C66A is detected during 2007 - 2008 in VHE (very high energy: E > 100 GeV) gamma-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, in these observations (32.8 hours live time). The observed integral flux above 200 GeV is 6 % of the Crab Nebula's flux and shows evidence for variability on a time-scale of days. The measured energy spectrum is characterized by a soft power law with photon index Gamma = 4.1 +/- 0.4stat +/- 0.6sys. The radio galaxy 3C66B is excluded as a possible source of the VHE emission.