Active Galactic Nuclei at the Highest Gamma-Ray Energies

In this talk, I will present some results from gamma-ray observations of active galactic nuclei (AGN) with the Very Energetic Radiation Imaging Telescope Array System (VERITAS), a state-of-the-art TeV gamma-ray observatory. Following a brief introduction on the experimental techniques, I will describe recent discoveries of rapid (minute-scale) gamma-ray flaring of AGN. Such variability has provided new insights, in a relatively model-independent manner, into gamma-ray production and propagation in the jets of AGN. The results have presented serious challenges to theoretical models. Gamma-ray emitting AGN may also be used as background sources to probe the intervening extragalactic infrared radiation background, which carries information on galaxy formation and evolution. The results are highly constraining. I will end the talk by discussing future outlook and the roles that China may play in the field of ground-based gamma ray astrophysics