Executive Summary : | Active galactic nuclei (AGN) make up 40% of sources detected at very high energies with Atmospheric Cherenkov telescopes (ACTs). About 1% of all galaxies host an active nucleus, which emits extremely bright emissions of the entire electromagnetic spectrum. Around 10% of AGN show powerful collimated relativistic jets emerging from the nucleus, dominated by non-thermal radiation. If these jets are oriented very close to the Earth's line of sight, they are classified as blazars. Blazars help understand particle acceleration at the inner jet, as the dominant part of the observed non-thermal emission originates close to the central engine. Recent detections of minute-scale gamma-ray variability and peak-in-peak flare patterns in blazar light curves challenge the shock-in-jet scenario. The recent detection of very hard photon spectrum from Fermi-LAT and MAGIC telescopes has challenged the current understanding of the origin of gamma-ray emission and particle acceleration mechanisms in blazars. These findings are difficult to reconcile with the conventional interpretation of canonical shock-in-jet models of blazars and have given rise to more sophisticated scenarios, such as turbulence, magnetic reconnection, or emission from the magnetosphere of a black hole. To improve our understanding of particle acceleration, gamma-ray emission mechanism and location, and jet launching mechanisms, multi-wavelength (MW) campaigns of blazars and radio galaxies are proposed. These campaigns will provide high-quality spectral and time-resolved flux information, and will strengthen our understanding of particle acceleration, jet launching, and radiation mechanisms of blazars and radio galaxies. |