TeV Neutrinos and Hard X-Rays from Relativistic Reconnection in the Corona of NGC 1068

Journal Article · Mon Jan 15 00:00:00 EST 2024 · The Astrophysical Journal. Letters

DOI:https://doi.org/10.3847/2041-8213/ad192b· OSTI ID:2281283

Fiorillo, Damiano F. G. ; Petropoulou, Maria ; Comisso, Luca ; Peretti, Enrico ; Sironi, Lorenzo

Abstract The recent discovery of astrophysical neutrinos from the Seyfert galaxy NGC 1068 suggests the presence of nonthermal protons within a compact “coronal” region close to the central black hole. The acceleration mechanism of these nonthermal protons remains elusive. We show that a large-scale magnetic reconnection layer, of the order of a few gravitational radii, may provide such a mechanism. In such a scenario, rough energy equipartition between magnetic fields, X-ray photons, and nonthermal protons is established in the reconnection region. Motivated by recent 3D particle-in-cell simulations of relativistic reconnection, we assume that the spectrum of accelerated protons is a broken power law, with the break energy being constrained by energy conservation (i.e., the energy density of accelerated protons is at most comparable to the magnetic energy density). The proton spectrum is ${\mathit{dn}}_p/{\mathit{dE}}_p\propto E_p^{-1}$ below the break and ${\mathit{dn}}_p/{\mathit{dE}}_p\propto E_p^{-s}$ above the break, with IceCube neutrino observations suggesting s ≃ 3. Protons above the break lose most of their energy within the reconnection layer via photohadronic collisions with the coronal X-rays, producing a neutrino signal in good agreement with the recent observations. Gamma rays injected in photohadronic collisions are cascaded to lower energies, sustaining the population of electron–positron pairs that makes the corona moderately Compton thick.

• Sponsoring Organization: USDOE
• Grant/Contract Number: SC0023015
• OSTI ID: 2281283
• Journal Information: The Astrophysical Journal. Letters, Journal Name: The Astrophysical Journal. Letters Vol. 961 Journal Issue: 1; ISSN 2041-8205
• Publisher: American Astronomical Society
• Country of Publication: United States
• Language: English