Precise location of high‑energy particle acceleration in M87

Determine the precise spatial location of the high‑energy particle acceleration site in M87 responsible for the April 2018 very high‑energy gamma‑ray emission, distinguishing whether it lies at event‑horizon scales imaged by the Event Horizon Telescope or in downstream inner‑jet regions, using contemporaneous multi‑wavelength and VLBI constraints.

Background

During the April 2018 Event Horizon Telescope campaign, M87 exhibited a very high‑energy (VHE) gamma‑ray flare alongside extensive multi‑wavelength coverage from radio to TeV energies. Despite compiling a contemporaneous spectral energy distribution and imaging the event‑horizon‑scale ring, the authors note that the precise site of the particle acceleration responsible for the VHE emission cannot yet be localized.

Identifying the acceleration site is critical for constraining jet launching mechanisms, magnetospheric models near the black hole, and the interpretation of VHE emission processes. The dataset provides strong constraints but leaves the exact spatial origin unresolved.