Fermi Gamma-ray Space Telescope

VERITAS AGN Observation Program

A. U. Abeysekara
for The VERITAS Collaboration

Abstract:

Active Galactic Nuclei (AGN) are the most prevalent class of identified very high energy (VHE; E > 100 GeV) gamma-ray emitting objects, making up nearly one-third of the TeVCat catalog. AGN emit non-thermal radiation across the electromagnetic spectrum from radio to VHE gamma rays, and the photon flux is highly variable in time scales from days to years. Simultaneous broad band multiwavelength observations of AGN can be used to constrain fundamental physics questions such as the absorption by the extragalactic background light and Lorentz Invariance Violations. The VERITAS observatory, an array of four 12-m imaging atmospheric-Cherenkov telescopes, spends on average ~425 h per year on observing AGN. Target-of-opportunity (ToO) observations have been given a high priority for observing AGN flaring states. Often the ToO are triggered from the low energy partners, or by automated analysis pipelines to monitor a selected set of Fermi-LAT detected AGN, and issue flaring alerts. Two ToO observations resulted in the VERITAS discovery of VHE emission from two blazars during the last observation season. Flaring states of several other known VHE emitting blazars were also detected. Independent from low energy partners, VERITAS also monitors known AGN for flaring states in the VHE regime. Highlights from the recent VERITAS AGN observation program, and future of the program are presented.