Speaker
Description
Since 2019, the Event Horizon Telescope (EHT) Collaboration released the first horizon-scale images of M87 and Sgr A, two primary EHT targets and the only systems resolved at horizon scales so far, while the innermost jet regions of a few (other) AGNi were explored at an unprecedented angular resolution. EHT campaigns are accompanied by extensive MWL observations, from radio up to very-high-energy (VHE) γ-rays. Combining EHT's direct horizon-scale imaging and polarization power with broadband MWL light curves and spectral energy distributions offers a unique opportunity to investigate the origin of the variable high-energy emission, the particle acceleration processes at play in the near-horizon plasma, and the disk-jet connection in general. H.E.S.S. has actively participated in these campaigns, along with other VHE γ-ray observatories.
In this talk, I review the lessons learned from the past campaigns on M87 and archetypal blazar 3C 279. The April 2017 3C 279 campaign combined ~20 μas EHT imaging with an extensive MWL data set, where a core flux increase was seen coincident with a superluminal knot ejection, preceded by record UV–optical flaring. Turbulent multi-zone jet model reproduces much of this behaviour, although alternative mechanisms remain possible. For M87, multi-year EHT observations now exist and span very different γ-ray states of the source. M87 and 3C 279 are known for occasional bright VHE and HE γ-ray flares, respectively, and together provide a valuable foundation for population studies in the growing sample of EHT-MWL targets.