The Interplay between accelerated Protons, X-rays and Neutrinos in the Corona of NGC 1068: Constraints from Kinetic Plasma Simulations

TL;DR

This study uses kinetic plasma simulations to explore how accelerated protons in NGC 1068's corona could produce the observed neutrino excess, highlighting the need for specific proton injection conditions and magnetic turbulence.

Contribution

It demonstrates that protons from the thermal pool cannot explain neutrino observations, proposing a scenario involving pre-acceleration in magnetic reconnection regions near the black hole.

Findings

Coronal X-rays absorb hadronic gamma rays within 100 Schwarzschild radii.

Protons from the thermal pool are insufficient to produce observed neutrinos.

Pre-accelerated protons in magnetic reconnection sites can generate neutrino signals consistent with IceCube data.

Abstract

We examine properties of accelerated protons potentially responsible for the neutrino excess observed in the direction of NGC 1068, using constraints from kinetic Particle-in-Cell (PIC) simulations. We find that i) coronal X-rays and Optical/Ultra-Violet light in the inner disk lead to efficient absorption of hadronic $\gamma$-rays within 100 Schwarzschild radii from the black hole; ii) protons accelerated from the coronal thermal pool cannot account for the observed neutrinos; and iii) explaining the observed signal requires an injection of protons with a hard spectrum, peaking at $\gamma_p\sim 10^3-10^4$, into the turbulent magnetically-dominated corona, where they are confined and re-accelerated. The resulting neutrino signal can be consistent with IceCube observations. In our most favorable scenario, the injected protons are pre-accelerated in intermittent current sheets in the vicinity of the black hole, occurring either at the boundary between the disk and the outflow or during magnetic flux eruption events.