Which active galaxies might be neutrino emitters?

TL;DR

This study suggests that active galactic nuclei with higher X-ray flux and greater mid-infrared variability are more likely to be neutrino sources, highlighting the importance of long-term fluctuations in the central engine for neutrino production.

Contribution

It introduces the correlation between MIR variability and neutrino emission in AGNs, proposing long-term fluctuations as a key factor in neutrino production, which was not emphasized before.

Findings

High-confidence neutrino emitters have higher X-ray fluxes.

Neutrino emitters show more MIR variability than other AGNs.

Long-term AGN fluctuations may be critical for neutrino production.

Abstract

The IceCube Neutrino Observatory has identified several individual neutrino emitters associated with supermassive black hole accretion phenomena, including blazars, tidal disruption events, and, unexpectedly, Seyfert galaxies. A key open question is which types of active galactic nuclei (AGNs) are most likely to be neutrino emitters. Here we show that high-confidence extragalactic neutrino emitters tend not only to have higher hard X-ray fluxes but also to be more variable in mid-infrared (MIR) than other AGNs in the \textit{Swift} BAT AGN Spectroscopic Survey. MIR variations effectively trace long-term fluctuations in AGN accretion disks and/or jets. In addition to the role of X-ray flux emphasized in previous studies, we speculate that long-term central engine fluctuations may also be critical for neutrino production. This hypothesis may inform IceCube neutrino-electromagnetic counterpart association studies and provide new insights into cosmic ray acceleration sites. First, the observed neutrinos are unlikely to originate from AGN host galaxies or from interactions between large-scale (dozens of parsecs) winds/outflows and the surrounding interstellar medium. Second, if neutrinos are produced in the X-ray corona, the corona should exhibit strong magnetic turbulence dissipation or magnetic reconnection whose rate changes substantially on timescales of years. Third, the relativistic jets of blazar neutrino emitters may be intrinsically unstable over years. Finally, if neutrinos are related to interactions between small-scale winds/outflows and torus clouds, such winds/outflows must be highly episodic.