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Diffuse neutrino flux from coronal magnetospheric current sheets of accreting black holes

Despina Karavola, Maria Petropoulou, Damiano F. G. Fiorillo, Luca Comisso, Lorenzo Sironi

TL;DR

This study investigates whether protons accelerated in magnetospheric current sheets of accreting black holes can power AGN coronae and contribute to the diffuse high-energy neutrino background. It introduces a photohadronic coronal framework with two key parameters, $σ_p$ and $λ_{X,Edd}$, and derives a population-level neutrino flux by applying spectral templates to a combined AGN catalog. The results show that $σ_p = 10^5$ reproduces the IceCube diffuse neutrino spectrum in both flux and slope, with NGC 1068 as a prominent contributor. This work links coronal magnetization and accretion physics to the high-energy neutrino background and highlights calorimetric effects at high fields as a direction for future work.

Abstract

Non-jetted AGN exhibit hard X-ray emission with a power law spectrum above $\sim$2 keV, which is thought to be produced through Comptonization of soft photons by electrons and positrons (pairs) in the vicinity of the black hole. The origin and composition of this plasma source, known as the corona, is a matter open for debate. Our study focuses on the role of relativistic protons accelerated in black-hole magnetospheric current sheets in the neutrino production of AGN coronae. We present a model that has two free parameters, namely the proton plasma magnetization $σ_{\rm p}$, which controls the peak energy of the neutrino spectrum, and the Eddington ratio $λ_{\rm Edd}$ (defined as the ratio between X-ray luminosity $L_{\rm X}$ and Eddington luminosity $L_{\rm Edd}$), which controls the amount of energy transferred to secondary particles. Furthermore, we combine our coronal model with an AGN population in order to provide a prediction for the diffuse neutrino flux measured on Earth. We compare our results with the observational data by IceCube and we find a satisfactory agreement on both the flux value and the slope of the neutrino distribution when we assume a $σ_{\rm p}$ value of $10^5$ for all the sources in our sample.

Diffuse neutrino flux from coronal magnetospheric current sheets of accreting black holes

TL;DR

This study investigates whether protons accelerated in magnetospheric current sheets of accreting black holes can power AGN coronae and contribute to the diffuse high-energy neutrino background. It introduces a photohadronic coronal framework with two key parameters, and , and derives a population-level neutrino flux by applying spectral templates to a combined AGN catalog. The results show that reproduces the IceCube diffuse neutrino spectrum in both flux and slope, with NGC 1068 as a prominent contributor. This work links coronal magnetization and accretion physics to the high-energy neutrino background and highlights calorimetric effects at high fields as a direction for future work.

Abstract

Non-jetted AGN exhibit hard X-ray emission with a power law spectrum above 2 keV, which is thought to be produced through Comptonization of soft photons by electrons and positrons (pairs) in the vicinity of the black hole. The origin and composition of this plasma source, known as the corona, is a matter open for debate. Our study focuses on the role of relativistic protons accelerated in black-hole magnetospheric current sheets in the neutrino production of AGN coronae. We present a model that has two free parameters, namely the proton plasma magnetization , which controls the peak energy of the neutrino spectrum, and the Eddington ratio (defined as the ratio between X-ray luminosity and Eddington luminosity ), which controls the amount of energy transferred to secondary particles. Furthermore, we combine our coronal model with an AGN population in order to provide a prediction for the diffuse neutrino flux measured on Earth. We compare our results with the observational data by IceCube and we find a satisfactory agreement on both the flux value and the slope of the neutrino distribution when we assume a value of for all the sources in our sample.

Paper Structure

This paper contains 5 sections, 9 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Coronal model
  3. Galaxy sample
  4. Diffuse neutrino flux
  5. Discussion

Figures (2)

  • Figure 1: Scatter plots showing the X-ray luminosity distribution (panel a), the X-ray Eddington ratio (panel b), the black hole mass (panel c), and the X-ray flux (panel d) as a function of luminosity distance for sources from the BAT catalog (colored circles) and the mock AGN catalog (colored crosses). Color shows the black hole mass for both populations (see colorbars).
  • Figure 2: All-flavor neutrino energy flux of non-blazar AGN in the catalog of ricci_bat_2017 for three $\sigma_{\rm p}$ values, namely $10^3$ (top panel), $10^5$ (middle panel) and $10^7$ (bottom panel). Normalization scales as described by eq. \ref{['eq:mock_sample']}. Colored curves show neutrino spectra from a sub-sample of the mock catalog. Colors represent the ratio $\lambda_{\rm \rm X, Edd}$. The dashed black line shows the sum of all sources while the dash-doted black one represents the contribution of all the sources in the BAT catalog. Finally, the red dotted line with downward pointing arrows represents the neutrino flux upper limits for non-blazar sources from Table 1 of abbasi_search_2024 and the black markers indicate the diffuse neutrino flux observed by IceCube naab_measurement_2023.