Fast γ-ray Variability: A Common Feature and Powerful Probe for Jetted AGNs

Abstract

Among the highly dynamical non-thermal universe, flashes of γ-ray photons from jets in active galactic nuclei (AGNs) are always attractive. Not only are they extraordinary observational phenomena, but they also become powerful probes of the jets. Benefiting from the current advanced γ-ray observational facilities, especially the Large Area Telescope aboard the Fermi space γ-ray observatory and Imaging Atmospheric Cherenkov Telescope arrays, fast (intraday) γ-ray variability has become a common feature detected in various subtypes of jetted AGNs. Moreover, extreme events with variability timescales down to a few minutes have been occasionally detected, which put a severe constraint on the classical jet model. Herein, recent studies on the detection of fast γ-ray variability in jetted AGNs are summarized, and corresponding implications are discussed. Scenarios proposed to explain the minute-scale γ-ray variability as well as future observational opportunities are also briefly summarized.

Keywords

• galaxies: active
• galaxies: jets
• gamma rays: general
• radiation mechanisms: non-thermal