Structured jets in BL Lac objects: efficient PeV neutrino factories?

TL;DR

This paper investigates whether structured jets in BL Lac objects can serve as efficient PeV neutrino factories, potentially explaining IceCube's high-energy neutrino observations through enhanced photo-meson reactions.

Contribution

It demonstrates that velocity-structured jets in BL Lacs can significantly boost neutrino production via photo-meson interactions, aligning theoretical predictions with IceCube data.

Findings

Neutrino output can be amplified by jet velocity structure.

Predicted diffuse neutrino intensity matches IceCube observations.

Enhanced inverse Compton emission correlates with neutrino production.

Abstract

The origin of the high-energy neutrinos (0.1$-$1 PeV range) detected by IceCube remains a mystery. In this work we explore the possibility that efficient neutrino production can occur in structured jets of BL Lac objects, characterized by a fast inner spine surrounded by a slower layer. This scenario has been widely discussed in the framework of the high-energy emission models for BL Lacs and radiogalaxies. One of the relevant consequences of a velocity structure is the enhancement of the inverse Compton emission caused by the radiative coupling of the two zones. We show that a similar boosting could occur for the neutrino output of the spine through the photo-meson reaction of high-energy protons scattering off the amplified soft target photon field of the layer. Assuming the local density and the cosmological evolution of $\gamma$-ray BL Lac derived from {\it Fermi}-LAT data, we calculate the expected diffuse neutrino intensity, that can match the IceCube data for a reasonable choice of the parameters.