Testing the Association of Supermassive Black Hole Infrared Flares and High-energy Neutrinos

The physical origin of the observed cosmic neutrinos remains an open question and the subject of active research. While matter accretion onto supermassive black holes is long thought to accelerate particles to high energies, it has recently been suggested that tidal disruption events, and accretion flares in general, with prominent IR echoes can account for a fraction of the diffuse high-energy neutrino signal. Motivated by this result, we compile a sample of nearby accretion flares detected in the NEOWISE survey featuring strong IR echoes, and we cross-match it with the latest catalog of neutrino alerts, IceCat-1. We recover only a single spatial coincidence between the two catalogs, consistent with a chance coincidence. We find no temporal and spatial coincidences between the two samples, which, given the properties of our sample, appears to challenge previous conclusions. We discuss the physical implications of our results and potential future explorations.

💡 Research Summary

The paper presents a systematic test of the proposed link between infrared (IR) flares from supermassive black holes (SMBHs) and high‑energy neutrinos detected by IceCube. Motivated by recent claims that dust‑reprocessed IR echoes of tidal disruption events (TDEs) and other accretion flares could account for a sizable fraction of the diffuse astrophysical neutrino flux, the authors assembled two independent data sets. First, they built a catalog of 99 nearby (z < 0.05, within 200 Mpc) nuclear IR transients using the NEOWISE mission. Candidate selection required (i) a positional match within 2 arcsec of a galaxy nucleus from the CLU catalog, (ii) a duration longer than two years to exclude typical supernovae, (iii) a fractional rms variability Fvar ≥ 0.1, and (iv) a brightening of at least Δm < −0.2 mag relative to a pre‑flare baseline. This pipeline preferentially isolates high‑amplitude, fast‑rising, slowly declining accretion flares, many of which lack optical counterparts and are therefore likely heavily dust‑obscured.

Second, they used the IceCat‑1 catalog of IceCube neutrino alerts, selecting 68 track‑like events from 2014 onward (the start of the NEOWISE re‑activation) with signalness > 0.5 and 90 % angular uncertainties ≤ 50°. The authors then performed a spatial cross‑match, requiring the IR flare position to fall inside the 90 % error contour of a neutrino event, and a temporal match, defined conservatively as the neutrino arrival occurring within one year of the IR flare’s peak flux. This temporal window follows earlier studies that found neutrinos clustered around the IR peak of TDEs.

The analysis yielded only a single spatial coincidence (WTP14aczncp with IC140721A), but the neutrino arrived during a low‑flux phase of the IR source, well before the flare’s peak, making a physical association implausible. Consequently, the authors report zero complete space‑time coincidences between their IR flare sample and high‑signalness neutrinos.

To assess whether the lack of matches contradicts previous work, they computed the peak‑minus‑baseline IR flux (ΔFIR) for each flare and compared the distribution to that of optically selected flares used by van Velzen et al. (2024). Their IR‑selected flares have systematically higher ΔFIR, yet none are associated with neutrinos, whereas van Velzen et al. reported several coincidences. Assuming a linear correlation between IR flux (as a proxy for bolometric output) and neutrino flux, the authors would have expected several matches given their sample size and flux levels. The absence of any suggests that the assumed correlation may be oversimplified, that neutrino production may be tied to earlier UV/optical phases rather than the dust‑reprocessed IR peak, or that selection biases (e.g., exclusion of known TDEs not in CLU) affect the results.

Statistically, the expected number of random coincidences for 99 flares and 68 neutrinos is ≈0.7; observing zero is consistent with pure chance but challenges the claim that ~20 % of IceCube events arise from accretion flares. The authors discuss limitations such as IceCube’s angular resolution, the modest number of alerts, and the possibility that only a subset of flares (perhaps those with specific jet or magnetic field properties) produce neutrinos.

Future directions include: (1) deeper, higher‑cadence IR monitoring with facilities like JWST or SPHEREx to capture fainter or faster dust echoes; (2) coordinated multi‑wavelength follow‑up (optical, UV, X‑ray) to pinpoint the exact phase of particle acceleration; (3) leveraging next‑generation neutrino detectors (IceCube‑Gen2, KM3NeT) with improved localization and sensitivity; and (4) expanding the host‑galaxy catalog to include more southern sky objects and known TDEs omitted here. By integrating these approaches, the community can more robustly test whether transient SMBH accretion events contribute significantly to the high‑energy neutrino sky.