Baryon Loading Efficiency and Particle Acceleration Efficiency of Relativistic Jets: Cases For Low Luminosity BL Lacs

TL;DR

This study analyzes the baryon loading and particle acceleration efficiencies in low luminosity BL Lac jets, revealing their limited capacity to produce ultra-high-energy cosmic rays within the one-zone SSC model framework.

Contribution

It provides new estimates of jet power, efficiency, and particle acceleration parameters for HBLs, highlighting their inefficiency in UHECR production.

Findings

HBLs have P_B/P_e~6.3×10^{-3} and radiative efficiency ~6.7×10^{-4}

Jet power relates to black hole mass as P_jet/L_Edd~0.18

Particle acceleration efficiency η_g~10^{4.5} indicating inefficiency for UHECR acceleration

Abstract

Relativistic jets launched by supermassive black holes, so-called as active galactic nuclei (AGNs), are known as the most energetic particle accelerators in the universe. However, the baryon loading efficiency onto the jets from the accretion flows and their particle acceleration efficiencies have been veiled in mystery. With the latest data sets, we perform multi-wavelength spectral analysis of quiescent spectra of 13 TeV gamma-ray detected high-frequency-peaked BL Lacs (HBLs) following one-zone static synchrotron-self-Compton (SSC) model. We determine the minimum, cooling break, and maximum electron Lorentz factors following the diffusive shock acceleration (DSA) theory. We find that HBLs have $P_B/P_e\sim6.3\times10^{-3}$ and the radiative efficiency $\epsilon_{\rm rad,jet}\sim6.7\times10^{-4}$ where $P_B$ and $P_e$ is the Poynting and electron power, respectively. By assuming 10 leptons per one proton, the jet power relates to the black hole mass as $P_{\rm jet}/L_{\rm Edd}\sim0.18$ where $P_{\rm jet}$ and $L_{\rm Edd}$ is the jet power and the Eddington luminosity, respectively. Under our model assumptions, we further find that HBLs have the jet production efficiency of $\eta_{\rm jet}\sim1.5$ and the mass loading efficiency of $\xi_{\rm jet}\gtrsim5\times10^{-2}$. We also investigate the particle acceleration efficiency in the blazar zone by including the most recent Swift/BAT data. Our samples ubiquitously have the particle acceleration efficiency of $\eta_g\sim10^{4.5}$, which is inefficient to accelerate particles up to the ultra-high-energy-cosmic-ray (UHECR) regime. This implies that the UHECR acceleration sites should be other than the blazar zones of quiescent low power AGN jets, if one assumes the one-zone SSC model based on the DSA theory.