The Composition and Power of the Jet of the Broad-Line Radio Galaxy 3C 120

TL;DR

This study analyzes the composition and power of the jet in 3C 120, finding it likely to be pair-dominated and examining its magnetic flux and energetics through observational data and theoretical models.

Contribution

It provides evidence that the jet of 3C 120 is pair-dominated and compares jet power with theoretical limits, offering new insights into jet composition and magnetic flux.

Findings

Jet is likely pair-dominated based on pair production rates.

Jet power exceeds magnetically arrested disk limits unless pairs dominate.

Magnetic flux matches the maximum poloidal flux threading the black hole.

Abstract

We calculated the electron-positron pair production rate at the base of the jet of 3C 120 by collisions of photons from the hot accretion flow using the measurement of its average soft gamma-ray spectrum by Compton Gamma Ray Observatory. We found that this rate approximately equals the flow rate of the leptons emitting the observed synchrotron radio-to-IR spectrum of the jet core, calculated using the extended jet model following Blandford \& Konigl. This coincidence shows the jet composition is likely to be pair-dominated. We then calculated the jet power in the bulk motion of ions, and found it greatly exceeds that achievable by the magnetically arrested disk scenario for the maximum black hole spin unless the jet contains mostly pairs. Next, we found that the magnetic flux through the synchrotron-emitting jet equals the maximum poloidal flux that can thread the black hole. Finally, we compared two estimates of the magnetization parameter at the onset of the synchrotron emission and found they are in agreement only if pairs dominate the jet content.