Origin of M87’s VHE gamma‑ray emission

Ascertain the physical origin of the very high‑energy gamma‑ray emission from M87 across both flaring and quiescent states by determining the dominant emission mechanism (e.g., leptonic versus hadronic processes) and the emitting region (e.g., black‑hole magnetosphere, inner jet, or downstream knots).

Background

M87 has shown multiple VHE gamma‑ray flares (2005, 2008, 2010) and a new flare in 2018, yet consistent, multi‑epoch multi‑wavelength observations and modeling have not yielded a definitive physical origin for the VHE emission.

The paper presents contemporaneous VHE detections and compares them to historical flares but concludes that the underlying mechanism and location remain unresolved despite prior campaigns.

References

Despite deep investigations of past flaring episodes of the source as well as of the quiescent state during the 2017 EHT campaign (M87 MWL2017), the origin of the VHE y-ray emission from M87 is still unclear.

— Broadband Multi-wavelength Properties of M87 during the 2018 EHT Campaign including a Very High Energy Flaring Episode  (2404.17623 - Algaba et al., 2024) in Section 3.3.1 VHE gamma ray flaring episode

Although \citet{2026ApJ..1003...71Y} suggest that the TeV flux can be explained by leptohadronic emission from winds, the wind energetics are not explicitly presented, and thus, it remains uncertain whether winds in the LLAGN can account for the TeV emission during the quiet period.

— TeV Gamma Rays and Neutrinos from Winds Driven by Radiatively Inefficient Accretion Flows of Low-Luminosity Active Galactic Nuclei  (2608.30596 - Sakai et al., 31 Aug 2026) in Section 1, Introduction