The power of the jets accelerated by the coronal magnetic field

TL;DR

This paper estimates the maximum power of jets driven by coronal magnetic fields in accretion disks, finding it insufficient to explain the most powerful observed jets in blazars, and suggests alternative magnetic mechanisms involving the accretion disk.

Contribution

It provides a quantitative estimate of jet power from coronal magnetic fields and compares it with observed jet powers, highlighting limitations of the coronal mechanism.

Findings

Blandford-Payne jet power exceeds Blandford-Znajek power except for rapidly spinning black holes.

Maximum jet power from the coronal magnetic field is less than 0.05 Eddington luminosity.

Coronal magnetic fields alone cannot account for the most powerful jets in blazars.

Abstract

It was suggested that the large scale magnetic field can be dragged inwards efficiently by the corona above the disc, i.e., the so called "coronal mechanism" (Beckwith, Hawley, \& Krolik 2009), which provides a way to solve the difficulty of field advection in a geometrically thin accretion disc. In this case, the magnetic pressure should be lower than the gas pressure in the corona. We estimate the maximal power of the jets accelerated by the magnetic field advected by the corona. The Blandford-Payne (BP) jet power is found always to be higher than the Blandford-Znajek (BZ) jet power, except for a rapidly spinning black hole with a>0.8. The maximal jet power is always low, less than 0.05 Eddington luminosity, even for an extreme Kerr black hole, which is insufficient for the observed strong jets in some blazars with jet power $\sim 0.1-1$ Eddington luminosity (or even higher). It implies that these powerful jets cannot be accelerated by the coronal field. We suggest that, the magnetic field dragged inward by the accretion disc with magnetically outflows may accelerate the jets (at least for the most powerful jets, if not all) in the blazars.