Prof Lucy Fortson

Gamma-rays can provide us with a view of the non-thermal Universe characterized by extreme phenomena including the jets of relativistic particles associated with radio-loud Active Galactic Nuclei (AGN) extending to kiloparsec and even megaparsec scales. A better understanding of these jets could help provide answers to disparate questions from the role of AGN feedback in cosmic evolution to the long-sought origin of ultra-high-energy cosmic rays. Operating for the past fifteen years, Imaging Air Cherenkov Telescopes – such as those comprising the four-telescope VERITAS array – have compiled a catalog of 275 sources, nearly 90 of which are AGN emitting Very-High-Energy (VHE ≥ 100 GeV) photons. These sources emit radiation spanning the entire observable electromagnetic spectrum and can vary in intensity over a wide range of timescales, from minutes to years. Understanding these VHE sources in the context of their broadband spectral energy distribution, as well as timing information from both simultaneous observations of flares and long-term monitoring campaigns, can help us understand fundamental properties of the jets themselves.  In this talk, I will draw from several examples of VERITAS-detected radio-loud AGN and associated multi-wavelength analyses to provide a snapshot of what we are learning in regards to the location of gamma-ray emitting regions in the jet, what the acceleration mechanisms are for the underlying particle populations, and whether a population of extreme blazars exists. I will close with a few words about the upcoming Cherenkov Telescope Array and the importance of gamma-ray observatories in the multi-messenger era.