High-energy Neutrinos from the Inner Circumnuclear Region of NGC 1068

TL;DR

This paper investigates the origin of high-energy neutrinos detected from NGC 1068, proposing that jet-ISM interactions in the galaxy's inner region could be significant neutrino sources, with models predicting observable sub-TeV gamma-ray signatures.

Contribution

It introduces a model linking jet-ISM interactions in NGC 1068 to observed neutrino fluxes, highlighting a potential hidden gamma-ray component for future detection.

Findings

Neutrino flux exceeds gamma-ray upper limits, constraining production sites.

Jet-ISM interactions may be key neutrino sources in NGC 1068.

Model predicts a detectable sub-TeV gamma-ray component.

Abstract

High-energy neutrinos are detected by the IceCube Observatory in the direction of NGC 1068, the archetypical type II Seyfert galaxy. The neutrino flux, surprisingly, is more than an order of magnitude higher than the $\gamma$-ray upper limits at measured TeV energy, posing tight constraints on the physical conditions of a neutrino production site. We report an analysis of the sub-millimeter, mid-infrared, and ultraviolet observations of the central $50$ pc of NGC 1068 and suggest that the inner dusty torus and the region where the jet interacts with the surrounding interstellar medium (ISM) may be a potential neutrino production site. Based on radiation and magnetic field properties derived from observations, we calculate the electromagnetic cascade of the $\gamma$-rays accompanying the neutrinos. When injecting protons with a hard spectrum, our model may explain the observed neutrino flux above $\sim 10$ TeV. It predicts a unique sub-TeV $\gamma$-ray component, which could be identified by a future observation. Jet-ISM interactions are commonly observed in the proximity of jets of both supermassive and stellar-mass black holes. Our results imply that such interaction regions could be $\gamma$-ray obscured neutrino production sites, which are needed to explain the IceCube diffuse neutrino flux.