The VERITAS Extragalactic Science Program

TL;DR

VERITAS is a gamma-ray observatory that studies extragalactic objects, especially AGN, providing insights into jet structures, classifying blazars, constraining the EBL, and discovering new gamma-ray sources like M82.

Contribution

This paper summarizes VERITAS's contributions to extragalactic gamma-ray astronomy, including AGN studies, blazar classification, EBL constraints, and discovery of non-AGN gamma-ray sources.

Findings

Insights into jet inner structures of AGN

Constraints on extragalactic background light

Discovery of gamma-ray emission from starburst galaxy M82

Abstract

VERITAS is an array of four 12-m diameter imaging atmospheric-Cherenkov telescopes located in southern Arizona. Its aim is to study the very high energy (VHE: E > 100 GeV) gamma-ray emission from astrophysical objects. The study of Active Galactic Nuclei (AGN) is intensively pursued through the VERITAS blazar key science project, but also through the large MWL observational campaigns on radio galaxies. The successful VERITAS AGN research program has provided insights to the jet inner structures and started a more detailed classification of blazars. Moreover, the synergy between Fermi and VERITAS on blazar observations resulted in important constraints on the extragalactic background light (EBL) through gamma-ray observations, and on the cataloguing of the several AGN sub-classes . VERITAS discovered also the first extragalactic non-AGN gamma-ray source. The discovery of gamma-ray emission from the starburst galaxy M 82 by VERITAS and Fermi provides important clues on possible mechanisms for accelerating cosmic rays.