MAD accretion and AGN jets -- an observational perspective

TL;DR

This paper explores how the magnetic flux in accreting black holes influences jet power, focusing on magnetically arrested disks and proposing VLBI core-shift measurements as a testing method.

Contribution

It introduces a method to test the role of magnetic flux in jet production using VLBI core-shift measurements, linking MADs to jet efficiency.

Findings

Magnetic flux threading black holes may determine jet power.

VLBI core-shift measurements can estimate jet magnetic flux.

Magnetically arrested disks are key to high-efficiency jet production.

Abstract

One of the major open questions related to the production of jets by accreting black holes is: why do sources with similar accretion powers produce so vastly different jet powers? What conditions are required to make a powerful jet? If jets are powered by the Blandford-Zjanek mechanism, two further parameters control the jet power besides the black hole mass - black hole spin and the magnetic flux threading it. Since highly spinning black holes without jets appear to exist, the jet production efficiency may depend on whether the black hole managed to accrete high enough magnetic flux in the past. The highest-efficiency jets in this picture are launched from magnetically arrested disks (MADs). Here we discuss a method to test this hypothesis using VLBI core-shift measurements to estimate the jet magnetic flux.