Multimessenger Characterization of High-Energy Neutrino Emission from the Brightest Neutrino-Active Galactic Nuclei

Abstract

The observation of high-energy neutrinos from the direction of the nearby active galaxy, NGC 1068, was a major step in identifying the origin of high-energy cosmic neutrinos. The multimessenger data imply that high-energy neutrinos originate from the hearts of active galaxies which are opaque to GeV-TeV $γ$-rays. This realization is reinforced by the excess of neutrinos in the direction of NGC 4151 and Circinus Galaxy, other nearby active galactic nuclei (AGNs). Understanding the vicinity of supermassive black holes with electromagnetic radiation is often challenging due to uncertainties associated with the absorption of emission in these dense environments, and neutrinos can be used as a powerful probe of the inner parts of the active galaxies. Considering the five brightest neutrino-active galaxies, NGC 1068, NGC 4151, CGCG 420-15, Circinus Galaxy, and NGC 7469, we employ the measured neutrino spectra together with the sub-GeV $γ$-ray emission measured by the {\em Fermi} satellite to break the degeneracy and narrow in on the parameter space of neutrino emission from turbulent coronae of AGNs. We also study contributions of jet-quiet AGNs, whose properties are similar to NGC 1068 and NGC 7469, to the isotropic neutrino background flux, through exploring possibilities that the neutrino luminosity function may deviate from the X-ray luminosity function. Our results will help estimate the prospects for identifying additional neutrino-active galaxies and guide future targeted analyses.

Figures (8)

• Figure 1: Left panel: Multi-dimensional MCMC for NGC 1068. $1\sigma,2\sigma$ and $3\sigma$ contours are shown. Median parameter values are shown as black dashed lines in the 1D histograms, along with their 68% band. Right panel: The all-flavor neutrino (red) and ${\gamma}$-ray fluxes (blue) for the MCMC parameters in the left panel. The $1\sigma$ and $3\sigma$ error bands for the fluxes are shown as shaded regions. The NGC 1068 power-law flux $1\sigma$ and $2\sigma$ containment regions are delineated by the solid and dotted black contours, respectively IceCube:2024dou. The observations from Fermi--LAT are shown as gray data points and are obtained from Ajello:2023hkh.
• Figure 2: Same as Figure \ref{['NGC1068_MCMC']}, but for NGC 4151. The $1\sigma$ containment region for the power-law fit is shown as a solid black contour IceCube:2024ayt. Observations from Fermi--LAT are obtained from Murase:2023ccp.
• Figure 3: Left panel: MCMC for CGCG 420-015. Right panel: Neutrino and ${\gamma}$-ray spectrum for the MCMC parameters. The $1\sigma$ and $3\sigma$ bands for the model flux are shown as shaded regions. The $1\sigma$ containment region for the power-law muon-neutrino flux hypothesis is marked by the black curve IceCube:2024ayt. Fermi bounds are from Ma:2025tpg.
• Figure 4: Left panel: MCMC for the Circinus Galaxy. Right panel: Neutrino and ${\gamma}$-ray using the MCMC chains, together with their $1\sigma$ bands. The $1\sigma$ band for the IceCube power-law fit is enclosed by the black lines IceCube:2026hzq. The Fermi-LAT ${\gamma}$-ray data points are from Murase:2023ccp.
• Figure 5: Left panel: MCMC for NGC 7469. Right panel: Neutrino and ${\gamma}$-ray spectrum for the MCMC parameters, together with their $1\sigma$ and $3\sigma$ bands. The $1\sigma$ band from the IceCube power-law fit is enclosed by the black lines Abbasi:2025tas and the ${\gamma}$-ray upper limits are from Yang:2025lmb.