Super-Accreting Active Galactic Nuclei as Neutrino Sources

Abstract

Active galactic nuclei (AGNs) often exhibit broad-line regions (BLRs), populated by high-velocity clouds in Keplerian orbits around the central supermassive black hole (SMBH) at subparsec scales. During episodes of intense super-Eddington accretion, the disk can launch a powerful radiation-driven wind that overtakes the BLR clouds, forming bowshocks. Two shocks arise: one into the wind and another into the cloud. If adiabatic, electrons and protons are efficiently accelerated via Fermi processes to relativistic energies. In dense winds, the resulting high-energy photons are absorbed and reprocessed within the photosphere, while neutrinos from inelastic $pp$ collisions escape. We explore the potential of super-accreting AGNs as neutrino sources and propose a new class of emitter: an AGN without jets or gamma-ray counterparts, but with a strong opaque disk wind. As a case study, we consider a SMBH with $M_{\rm BH}=10^6,M_{\odot}$ and accretion rates consistent with tidal disruption events (TDEs). We compute the main cooling processes for relativistic particles and show that super-Eddington SMBHs can produce detectable neutrino fluxes with only weak electromagnetic signatures. Such fluxes may be observable by IceCube-Gen2 in nearby galaxies with a high BLR cloud filling factor. For more massive black holes, detection remains possible with moderate filling factors if the source is close, or at larger distances if the filling factor is high. Our model thus provides a plausible scenario for extragalactic neutrino sources, where both flux and timescale are determined by the number of orbiting clouds and the duration of the super-accreting phase.