Jet-Driven Disk Accretion in Low Luminosity AGN?

TL;DR

This paper proposes a jet-driven accretion model for low luminosity AGN, explaining their low radiative output through low accretion rates and magnetic torques, and applies it to M87, matching observed spectra and jet power.

Contribution

It introduces a novel accretion model incorporating magnetic torques and jet formation, specifically tailored for low luminosity AGN like M87.

Findings

M87 may host a maximally spinning black hole.

Accretion rate is about 10^{-3} solar masses per year.

Predicted jet power aligns with observations.

Abstract

We explore an accretion model for low luminosity AGN (LLAGN) that attributes the low radiative output to a low mass accretion rate rather than a low radiative efficiency. In this model, electrons are assumed to drain energy from the ions as a result of collisionless plasma microinstabilities. Consequently, the accreting gas collapses to form a geometrically thin disk at small radii and is able to cool before reaching the black hole. The accretion disk is not a standard disk, however, because the radial disk structure is modified by a magnetic torque which drives a jet and which is primarily responsible for angular momentum transport. We also include relativistic effects. We apply this model to the well known LLAGN M87 and calculate the combined disk-jet steady-state broadband spectrum. A comparison between predicted and observed spectra indicates that M87 may be a maximally spinning black hole accreting at a rate of 10^{-3} solar masses per year. This is about 6 orders of magnitude below the Eddington rate for the same radiative efficiency. Furthermore, the total jet power inferred by our model is in remarkably good agreement with the value independently deduced from observations of the M87 jet on kiloparsec scales.