Establishing accretion flares from massive black holes as a source of high-energy neutrinos

TL;DR

This study suggests that accretion flares from supermassive black holes, including TDEs and AGN flares, are a significant source of high-energy neutrinos, with a potential contribution of at least 10% to IceCube alerts, indicating increased neutrino production efficiency during flares.

Contribution

The paper introduces the concept of accretion flares as a unified population of black hole activity that can produce high-energy neutrinos, supported by infrared dust echo observations and statistical association with IceCube events.

Findings

Identification of a third neutrino-associated accretion flare (AT2019aalc).

Estimated 3.6σ significance for neutrino-flare association.

At least 10% of IceCube high-energy neutrinos may originate from accretion flares.

Abstract

The origin of cosmic high-energy neutrinos remains largely unexplained. For high-energy neutrino alerts from IceCube, a coincidence with time-variable emission has been seen for three different types of accreting black holes: (1) a gamma-ray flare from a blazar (TXS 0506+056), (2) an optical transient following a stellar tidal disruption event (TDE; AT2019dsg), and (3) an optical outburst from an active galactic nucleus (AGN; AT2019fdr). For the latter two sources, infrared follow-up observations revealed a powerful reverberation signal due to dust heated by the flare. This discovery motivates a systematic study of neutrino emission from all supermassive black hole with similar dust echoes. Because dust reprocessing is agnostic to the origin of the outburst, our work unifies TDEs and high-amplitude flares from AGN into a population that we dub accretion flares. Besides the two known events, we uncover a third flare that is coincident with a PeV-scale neutrino (AT2019aalc). Based solely on the optical and infrared properties, we estimate a significance of 3.6$\sigma$ for this association of high-energy neutrinos with three accretion flares. Our results imply that at least ~10% of the IceCube high-energy neutrino alerts could be due to accretion flares. This is surprising because the sum of the fluence of these flares is at least three orders of magnitude lower compared to the total fluence of normal AGN. It thus appears that the efficiency of high-energy neutrino production in accretion flares is increased compared to non-flaring AGN. We speculate that this can be explained by the high Eddington ratio of the flares.