Hadronic signatures from magnetically dominated baryon-loaded AGN jets

TL;DR

This paper models hadronic signatures in magnetically dominated AGN jets, showing how jet magnetization and Lorentz factors influence photon and neutrino emissions, with implications for different blazar types.

Contribution

It introduces a numerical framework linking jet magnetization, Lorentz factor, and emission processes, highlighting the role of magnetic reconnection in particle energization.

Findings

Low-luminosity blazars have higher magnetization and resemble BL Lac objects.

High-luminosity blazars have lower magnetization and resemble flat spectrum radio quasars.

Neutrino luminosity correlates with gamma-ray luminosity, being higher in low-luminosity blazars.

Abstract

Blazars are a rare class of active galactic nuclei (AGN) with relativistic jets pointing towards the observer. Jets are thought to be launched as Poynting-flux dominated outflows that accelerate to relativistic speeds at the expense of the available magnetic energy. In this work, we consider electron-proton jets and assume that particles are energized via magnetic reconnection in parts of the jet where the magnetization is still high ($\sigma \ge 1$). The magnetization and bulk Lorentz factor $\Gamma$ are related to the available jet energy per baryon as $\mu =\Gamma(1+\sigma)$. We adopt an observationally motivated relation between $\Gamma$ and the mass accretion rate into the black hole $\dot{m}$, which also controls the luminosity of external radiation fields. We numerically compute the photon and neutrino jet emission as a function of $\mu$ and $\sigma$. We find that the blazar SED is produced by synchrotron and inverse Compton radiation of accelerated electrons, while the emission of hadronic-related processes is subdominant except for the highest magnetization considered. We show that low-luminosity blazars ($L_{\gamma} \lesssim 10^{45}$ erg s$^{-1}$) are associated with less powerful, slower jets with higher magnetizations in the jet dissipation region. Their broadband photon spectra resemble those of BL Lac objects, and the expected neutrino luminosity is $L_{\nu+\bar{\nu}}\sim (0.3-1)\, L_{\gamma}$. High-luminosity blazars ($L_{\gamma} \gg 10^{45}$ erg s$^{-1}$) are associated with more powerful, faster jets with lower magnetizations. Their broadband photon spectra resemble those of flat spectrum radio quasars, and they are expected to be dim neutrino sources with $L_{\nu+\bar{\nu}}\ll L_{\gamma}$.