Hillas meets Eddington: the case for blazars as ultra-high-energy neutrino sources
Context. Jetted active galactic nuclei aligned with our line of sight known as blazars are promising high-energy neutrino source candidates. However, leptohadronic models face challenges in describing neutrino emission within a viable energy budget and their predictive power are limited by the commo...
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| Main Authors: | , , , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
February 2026
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| In: |
Astronomy and astrophysics
Year: 2026, Volume: 706, Pages: 1-18 |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/202556986 |
| Online Access: | Verlag, kostenfrei, Volltext: https://doi.org/10.1051/0004-6361/202556986 Verlag, kostenfrei, Volltext: https://www.aanda.org/articles/aa/abs/2026/02/aa56986-25/aa56986-25.html 
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| Author Notes: | X. Rodrigues, F. Rieger, A. Bohdan, and P. Padovani |
| Summary: | Context. Jetted active galactic nuclei aligned with our line of sight known as blazars are promising high-energy neutrino source candidates. However, leptohadronic models face challenges in describing neutrino emission within a viable energy budget and their predictive power are limited by the commonly used single-zone approximation and reliance on phenomenological parameters. Aims. We tested the scenario where energetic protons are continuously accelerated up to ultra-high energies in inner blazar jets, while accounting for the source energetics and jet dynamics. Methods. We present a new leptohadronic model, where a sub-Eddington jet evolves from being magnetically to kinetically dominated. A constant fraction of 10 −6 -10 −8 of the electrons and protons picked up by the jet are continuously accelerated to a power-law spectrum. We can estimate their normalization and maximum energies based on the local magnetic field strength, turbulence, and medium density, for which we assumed power-law profiles. The model parameters are thus directly tied to the jet physics and are comparable in number to a single-zone model. We then calculate the emission along the jet, including neutrinos and electromagnetic cascades. Results. Applying the model to IceCube candidate TXS 0506+056, we find that protons accelerated in the inner jet produce a neutrino flux up to ∼100 PeV that is consistent with the public IceCube ten-year point-source data. Proton emission at 0.1 pc describes the X-ray and γ-ray data, while electron emission at the parsec scale describes the optical data. Protons carry a power of about 1% of the Eddington luminosity. The particle spectra follow E −1.8, with diffusion scaling as E 0.3, ruling out Bohm-like diffusion. Additional particle injection near the broad line region can reproduce the 2017 flare associated to a high-energy neutrino. We also applied the model to the blazar PKS 0605-085, which could be associated with a recent neutrino detected by KM3NeT above 100 PeV. Conclusions. Magnetic acceleration in blazar jets can describe multimessenger observations with viable energetics. Our model constrains jet properties such as the energy-dependent particle diffusion and predicts the spatial distribution of the multiwavelength and neutrino emission along the jet. The results suggest that blazars are efficient neutrino emitters at ultra-high energies, making them prime candidates for future experiments targeting this challenging energy range. |
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| Item Description: | Online veröffentlicht: 23. Februar 2026 Gesehen am 24.03.2026 |
| Physical Description: | Online Resource |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/202556986 |