Fundamental Reference AGN Monitoring Experiment (FRAMEx) III: Radio Emission in the Immediate Vicinity of Radio Quiet AGNs

TL;DR

This study investigates the radio and X-ray emissions of local AGNs, revealing most are undetected at high resolution, with emissions likely originating from low luminosity outflows or self-absorbed synchrotron radiation.

Contribution

It provides new high-resolution VLBA observations of local AGNs, showing the lack of correlation between radio and X-ray emissions and challenging existing black hole activity models.

Findings

Most AGNs are undetected at VLBA resolution.

No significant correlation between radio and X-ray luminosities.

Radio emission likely from low luminosity outflows or synchrotron self-absorption.

Abstract

We present follow-up results from the first Fundamental Reference AGN Monitoring Experiment (FRAMEx) X-ray/radio snapshot program of a volume-complete sample of local hard X-ray-selected active galactic nuclei (AGNs). Here, we added 9 new sources to our previous volume-complete snapshot campaign, two of which are detected in the 6 cm Very Long Baseline Array (VLBA) observations. We also obtained deeper VLBA observations for a sample of 9 AGNs not detected by our previous snapshot campaign. We recovered 3 sources with approximately twice the observing sensitivity. In contrast with lower angular resolution Very Large Array (VLA) studies, the majority of our sources continue to be undetected with the VLBA. The sub-parsec radio (6 cm) and X-ray (2-10 keV) emission show no significant correlation, with L_R/L_X ranging from 10^-8 to 10^-4, and the majority of our sample lies well below the fiducial 10^-5 relationship for coronal synchrotron emission. Additionally, our sources are not aligned with any of the proposed "fundamental" planes of black hole activity, which purport to unify black hole accretion in the M_BH-L_X-L_R parameter space. The new detections in our deeper observations suggest that the radio emission may be produced by the synchrotron radiation of particles accelerated in low luminosity outflows. Non-detections may be a result of synchrotron self-absorption at 6 cm in the radio core, similar to what has been observed in X-ray binaries (XRBs) transitioning from the radiatively inefficient state to a radiatively efficient state.