Lepto-hadronic single-zone models for the electromagnetic and neutrino emission of TXS 0506+056

TL;DR

This paper models the electromagnetic and neutrino emissions of the blazar TXS 0506+056 using lepto-hadronic single-zone models, finding that photo-hadronic cascades can explain neutrino observations better than proton synchrotron scenarios.

Contribution

It provides a detailed exploration of lepto-hadronic single-zone models for TXS 0506+056, comparing scenarios dominated by proton synchrotron and synchrotron-self-Compton emissions.

Findings

Photo-hadronic cascades can explain neutrino data.

Proton synchrotron models are disfavoured due to low neutrino production.

Extensive parameter space analysis of emission models.

Abstract

While active galactic nuclei with relativistic jets have long been prime candidates for the origin of extragalactic cosmic rays and neutrinos, the BL Lac object TXS 0506+056 is the first astrophysical source observed to be associated with some confidence ($\sim 3\sigma$) with a high-energy neutrino, IceCube-170922A, detected by the IceCube Observatory. The source was found to be active in high-energy gamma-rays with Fermi-LAT and in very-high-energy gamma-rays with the MAGIC telescopes. To consistently explain the observed neutrino and multi-wavelength electromagnetic emission of TXS 0506+056, we investigate in detail single-zone models of lepto-hadronic emission, assuming co-spatial acceleration of electrons and protons in the jet, and synchrotron photons from the electrons as targets for photo-hadronic neutrino production. The parameter space concerning the physical conditions of the emission region and particle populations is extensively explored for scenarios where the gamma-rays are dominated by either 1) proton synchrotron emission or 2) synchrotron-self-Compton emission, with a subdominant but non-negligible contribution from photo-hadronic cascades in both cases. We find that the latter can be compatible with the neutrino observations, while the former is strongly disfavoured due to the insufficient neutrino production rate.