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

Abstract

High-energy neutrinos have thus far been observed in coincidence with timevariable emission from three different accreting black holes: a gamma-ray flare from a blazar (TXS 0506+056), an optical transient following a stellar tidal disruption (AT2019dsg), and an optical outburst from an active galactic nucleus (AT2019fdr). Here we present a unified explanation for the latter two of these sources: accretion flares that reach the Eddington limit. A signature of these events is a luminous infrared reverberation signal from circumnuclear dust that is heated by the flare. Using this property we construct a sample of similar sources, revealing a third event coincident with a PeV-scale neutrino. This sample of three accretion flares is correlated with high-energy neutrinos at a significance of 3.7σ. Super-Eddington accretion could explain the high particle acceleration efficiency of this new population.Accreting black holes have long been suggested as potential sources of high-energy particles (1, 2) and this expectation was supported by the detection of a high-energy neutrino coincident (at the 3σ-level) with gamma-ray flaring from the blazar TXS 0506+056 (3). However, blazars alone cannot account for the observed high-energy neutrino flux (4, 5); similar to the electromagnetic sky, we can expect that the observed cosmic neutrino flux (6) arises from multiple source populations (7).In the last two years, optical follow-up observations of neutrino alerts (8) using the Zwicky Transient Facility (ZTF, ( 9)) have identified two optical flares from the centers of galaxies coincident with PeV-scale neutrinos: AT2019dsg (10) and AT2019fdr (11). The former belongs to the class of spectroscopically-classified tidal disruption events (TDEs) from quiescent black holes, while the latter originated from a type 1 (i.e., unobscured) active galactic nucleus (AGN).However, the distinctive shared properties we present below suggest these flares share a common origin.

Advancing the Landscape of Multimessenger Science in the Next Decade

“…This represents the first direct evidence of multi-messenger TDE emission, and accompanying modelling confirmed that conditions in these sources were consistent with requirements for the detection of a high-energy neutrinos [256][257][258][259]. An archival search has since identified AT2019aalc as a third candidate neutrino-TDE, with a combined statistical significance of 3.7σ [260]. A complimentary probe of TDE emission, searching for archival cross-correlation with neutrinos at ∼10 TeV energies, constrained the overall contribution of the TDE population to no more than 39% of the astrophysical neutrino flux under the assumption of an unbroken E −2.5 power law [261].…”

Could TDE outflows produce the PeV neutrino events?

“…After the submission of this work, we notice recent reports on more neutrino events associated with the time-variable emission from accreting SMBHs (van Velzen et al 2021a;Reusch et al 2021), among which AT2019fdr is a TDE candidate in a Narrow-Line Seyfert 1 AGN in which the BLR clouds should exist. Moreover, the neutrino events lag the optical outbursts by half one year to one year (van Velzen et al 2021a), consistent with the assumption that clouds exist at the distance of ∼ 10 −2 pc from the central BH if the outflow velocity is in the order of 10 9 cm s −1 .…”

“…There are signs that some clouds are located closely to the central SMBH in this source. AT2019dsg showed strong dust echo, which appears almost simultaneous with the burst in g-and r-band of ZTF (van Velzen et al 2021a). Considering that the dust echo flux is linearly proportional to the dust covering factor, the covering factor Cv should be around 10%.…”

GB6 J2113+1121: A multi-wavelength flaring gamma-ray blazar temporally and spatially coincident with the neutrino event IceCube-191001A

“…in GeV and TeV energies). Nevertheless, neutrinos are proposed be from the accretion flares in the super-Eddington systems, from which the lack of detecting γ-ray emissions are due to the severe γγ absorption (van Velzen et al 2021). Actually, evidences that the incoming neutrino events are associated with flaring blazars are cumulating.…”