IceCube's convex all-sky neutrino spectrum consistent with the magnetically powered corona scenario for active galactic nuclei

Abstract

High-energy multimessenger background analyses over the past decade have provided evidence for a population of hidden neutrino sources that are opaque to GeV-TeV gamma rays, a picture bolstered by recent observations of the nearby active galaxy NGC 1068. The coronal regions in the hearts of active galactic nuclei (AGNs) have been proposed as the most promising sites for such hidden nonthermal particle production, and NGC 1068 is expected to be the most neutrino-active galaxy for IceCube. We demonstrate that the latest all-sky neutrino spectrum, exhibiting a spectral bend around 3-30 TeV, is consistent with predictions of the magnetically powered corona scenario, and the models for the all-sky neutrino flux can simultaneously explain the multimessenger data from NGC 1068 within observational and modeling uncertainties. We further show, in a largely model-independent way, that the contribution from NGC 1068-like sources does not overshoot the observed medium-energy neutrino flux. Finally, we highlight the key role of the Eddington ratio, which can drive substantial variations in the predicted neutrino fluxes of nearby AGNs, and we encourage systematic multimessenger searches for the neutrino-brightest AGNs.

Figures (11)

• Figure 1: Summary of AGN models for all-sky neutrino and electromagnetic background fluxes. The original MKM20 model (Model A) Murase:2019vdl is shown by the solid curves (blue, red and purple). Model B and Model C (see text for details) are optimized for the latest IceCube data of medium-energy starting events IceCube:2025tgp (black) and enhanced starting track event selection IceCube:2024fxo (gray), respectively. The x-ray and soft gamma-ray data are taken from Swift BAT Ajello:2008xb (purple), Nagoya balloon 1975Natur.254..398F (yellow), SMM 1997AIPC..410.1223W (green), COMPTEL 2000AIPC..510..467W (orange), and Fermi LAT Ackermann:2014usa (red). Thick curves (AGN corona) represent neutrinos, gamma rays and x-rays from coronae of jet-quiet AGNs. Neutrinos and gamma rays including Comptonized RIAF (radiatively inefficient accretion flow) emission from low-luminosity AGNs are taken from Ref. Kimura:2020thg (LLAGN RIAF). Neutrino emission from jetted AGNs embedded in galaxy clusters and groups Fang:2017zjf and the sum of gamma rays from these objects and blazars Ajello:2013lka are also depicted (jetted AGN).
• Figure 2: All-sky neutrino and gamma-ray spectra for Model A (left panel), Model B (middle panel), and Model C (right panel). Note that the results for Model A are essentially the same as those presented in MKM20 except improved treatments of microphysics. The extragalactic neutrino, x-ray and gamma-ray background data are the same as those in Fig. \ref{['fig:summary']}.
• Figure 3: Cosmic-ray proton cooling time scales for coronae of jet-quiet AGNs with $L_X=10^{44}~{\rm erg}~{\rm s}^{-1}$ for Model A (left panel), Model B (middle panel), and Model C (right panel).
• Figure 4: Left panel: Differential cosmic-ray luminosities in for $L_X={10}^{42}$, ${10}^{43}$, ${10}^{44}$, ${10}^{45}$, and ${10}^{46}~{\rm erg}~{\rm s}^{-1}$ (from bottom to top). Right panel: Differential neutrino (thick) and gamma-ray (thin) luminosities in for $L_X={10}^{42}$, ${10}^{43}$, ${10}^{44}$, ${10}^{45}$, and ${10}^{46}~{\rm erg}~{\rm s}^{-1}$ (from bottom to top).
• Figure 5: X-ray luminosity dependence of the peak neutrino luminosity ($\varepsilon_\nu^{\rm pk}L_{\varepsilon_\nu^{\rm pk}}$) and the peak neutrino energy $\varepsilon_\nu^{\rm pk}$ for Model A (left panel), Model B (middle panel), and Model C (right panel). NGC 1068 and NGC 4151 are indicated by stars and diamonds, respectively.