Fermi Gamma-ray Space Telescope

Very-High-Energy Emission from Extragalactic Cosmic Accelerators - Highlights from recent VERITAS AGN Observations

Qi Feng
(The VERITAS Collaboration)


Nearly 5000 hours of observations of active galactic nuclei (AGN) have been performed over the decade-long operation of the Very Energetic Radiation Imaging Telescope Array System (VERITAS). These observations have led to 36 detections up to the redshift of 0.9, including some of the fastest and most energetic flares, which can provide strong constraints on the size and Doppler factor of the emitting regions that move at relativistic speed in AGN jets. Most of these observations are accompanied multiwavelength observations essential for studies of the emitting locations, the radiative processes, and the underlying particle populations in the jets of AGN. The gamma-ray observations of distant AGN can also provide cosmological constraints on the spectral energy distribution of the extragalactic background light (EBL) and the strength of the intergalactic magnetic field. Recent highlights from the VERITAS AGN observation program will be presented, including long-term and short-term variability of blazars, constraints on the EBL density, and the detections of a blazar potentially associated with astrophysical neutrinos, a new radio galaxy, and distant flat-spectrum radio qausars.