Fundamental Reference AGN Monitoring Experiment (FRAMEx). I. Jumping Out of the Plane with the VLBA

We present the first results from the Fundamental Reference active galactic nucleus (AGN) Monitoring Experiment, an observational campaign dedicated to understanding the physical processes that affect the apparent positions and morphologies of AGNs. In this work, we obtained simultaneous Swift X-ray Telescope and Very Long Baseline Array (VLBA) radio observations for a snapshot campaign of 25 local AGNs that form a volumecomplete sample with hard X-ray (14-195 keV) luminosities above 10(42) erg s(-1), out to a distance of 40.Mpc. Despite achieving an observation depth of similar to 20. mu Jy, we find that 16 of 25 AGNs in our sample are not detected with the VLBA on milliarcsecond (subparsec) scales, and the corresponding core radio luminosity upper limits are systematically below predictions from the Fundamental Plane of black hole activity. Using archival Jansky Very Large Array (VLA) radio measurements, our sample jumps back onto the Fundamental Plane, suggesting that extended radio emission is responsible for the apparent correlation between radio emission, X-ray emission, and black hole mass. We suggest that this discrepancy is likely due to extranuclear radio emission produced via interactions between the AGN and host environment. We compare VLBA observations of AGNs to VLA observations of nearby Galactic black holes, and we find a mass-independent correlation between radio and X-ray luminosities of black holes of L-6 (cm)/L-2- (10 keV) similar to 10(-6), in line with predictions for coronal emission, but allowing for the possibility of truly radio-silent AGNs.

Automated summary

The study presents results from an observational campaign dedicated to understanding the physical processes affecting the positions and morphologies of AGNs. Despite deep observations, 16 out of 25 AGNs in the sample were not detected on milliarcsecond scales, suggesting extended radio emission may play a role in the correlation between radio emission, X-ray emission, and black hole mass. Further comparisons between VLBA and VLA observations show a mass-independent correlation between radio and X-ray luminosities of black holes, indicating the possibility of truly radio-silent AGNs.