Speaker
Description
Seyfert galaxies have emerged as the most promising counterparts to TeV neutrino excesses detected by IceCube, with significant associations above the 3σ level. Stacked analyses of X-ray bright AGN further indicate a collective signal at ~3σ, supporting their contribution to the multi-messenger neutrino sky.
The AGN environment provides multiple sites capable of accelerating protons to the energies required to account for the observed neutrino flux. Gamma rays and neutrinos are co-produced through hadronic interactions between the accelerated protons and the ambient matter and radiation in the emission region.
However, radiation-dense regions like AGN cores efficiently absorb gamma rays, potentially suppressing part of the very-high-energy(VHE) emission(E>100 GeV). VHE gamma telescopes such as MAGIC are sensitive to an energy range similar to that of IceCube. Thus, they serve as an efficient probe to test the optical depth of these environments. VHE gamma-ray observations with the MAGIC telescopes of the most significant neutrino hotspot, NGC 1068, have already yielded stringent upper limits, revealing the presence of a gamma-ray obscured accelerator.
In this talk, we present observations of another promising neutrino counterpart, NGC 4151, and report the first upper limits on its VHE (E > 100 GeV) gamma-ray emission. The derived constraints limit the neutrino-emitting region up to ~10⁴ Schwarzschild radii of the central supermassive black hole. These results indicate that, similar to NGC 1068, NGC 4151 likely hosts a neutrino production site that is optically thick to gamma rays, supporting Seyfert galaxies as a potential class of hidden cosmic-ray accelerators.