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Neutrinos and Gamma Rays from Beta Decays in an Active Galactic Nucleus NGC 1068 Jet
Koichiro Yasuda1, Nobuyuki Sakai2, Yoshiyuki Inoue2,3,4
1University of California, Los Angeles, Department of Physics and Astronomy, Los Angeles, California 90095-1547, USA.
Physical Review Letters
|May 2, 2025
Summary
High-energy neutrinos and gamma rays from galaxy NGC 1068 are explained by neutron beta decays. This model, involving helium photodisintegration, aligns with observed gamma-ray deficits and can apply to other active galaxies.
Area of Science:
- Astrophysics
- Particle Astrophysics
- High-Energy Astrophysics
Background:
- Active galaxies like NGC 1068 emit high-energy neutrinos and gamma rays.
- Previous models often struggled to explain the observed fluxes simultaneously.
- Proton-photon interactions are a common explanation, but can lead to an overestimation of gamma-ray flux.
Purpose of the Study:
- To propose and validate a new model explaining the simultaneous detection of TeV neutrinos and high-energy gamma rays from NGC 1068.
- To investigate the role of nuclear photodisintegration and subsequent beta decays in active galactic nuclei jets.
- To reconcile the observed neutrino and gamma-ray fluxes with theoretical predictions.
Main Methods:
- Modeling the photodisintegration of Helium-4 nuclei by ultraviolet photons in the active galactic nuclei jet.
- Simulating the beta decay of photodisintegration-produced neutrons.
- Calculating the expected neutrino and gamma-ray fluxes from these processes.
- Comparing model predictions with observational data from NGC 1068.
- Considering synchrotron and inverse Compton emission from protons via Bethe-Heitler pair production and photopion processes.
Main Results:
- The model successfully explains the observed TeV neutrino energies (1-100 TeV) through neutron beta decays originating from Helium-4 photodisintegration at PeV energies.
- The predicted TeV gamma-ray flux from beta decays is significantly lower than the neutrino flux, consistent with the observed gamma-ray deficit in NGC 1068.
- The combined scenario, including proton-induced processes, can also explain the observed GeV gamma-ray flux for plausible jet magnetic field strengths.
- The proposed mechanism is applicable to other active galaxies, such as NGC 4151.
Conclusions:
- Neutron beta decays following Helium-4 photodisintegration offer a viable explanation for the observed TeV neutrinos and gamma rays from NGC 1068.
- This model resolves the gamma-ray deficit issue often encountered with proton-based models.
- Future neutrino flavor ratio measurements can provide crucial evidence for this beta-decay origin.
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