Exploring the accretion model of M87 and 3C 84 with the Faraday rotation measure observations

TL;DR

This study uses Faraday rotation measure observations to test accretion-jet models of LLAGNs M87 and 3C 84, finding that the jet-origin X-ray model aligns better with observations for M87, and that the sub-mm emission in 3C 84 is jet-dominated with an ADAF Faraday screen.

Contribution

It provides observational constraints on accretion-jet models of LLAGNs using RM data, distinguishing between ADAF and jet origins of X-ray and sub-mm emissions.

Findings

The ADAF-origin X-ray model for M87 predicts too high RM.

The jet-origin X-ray model for M87 matches RM observations.

In 3C 84, the sub-mm emission is jet-dominated with an ADAF Faraday screen.

Abstract

Low-luminosity active galactic nuclei (LLAGNs) are believed to be powered by an accretion-jet model, consisting of an inner advection-dominated accretion flow (ADAF), an outer truncated standard thin disk, and a jet. But model degeneracy still exists in this framework. For example, the X-ray emission can originate from either the ADAF or jet. The aim of the present work is to check these models with the Faraday rotation measure (RM) observations recently detected for two LLAGNs, M87 and 3C 84, in the sub-mm band. For M87, we find that the RM predicted by the model in which the X-ray emission originates from the ADAF is larger than the observed upper limit of RM by over two orders of magnitude, while the model in which the X-ray emission originates from the jet predicts a RM lower than the observed upper limit. For 3C 84, the sub-mm emission is found to be dominated by the jet component, while the Faraday screen is attributed to the ADAFs. This scenario can naturally explain the observed {\it external} origin of the RM and why RM is found to be stable during a two-year interval although the sub-mm emission increases at the same period.