Are the Jets Accelerated from the Disk Coronas in Some Active Galactic Nuclei?

We use a sample of radio-loud active galactic nuclei (AGNs) with estimatedcentral black hole masses to explore their jet formation mechanisms. The jetpower of AGNs is estimated from their extended radio luminosity. It is foundthat the jets in several AGNs of this sample are too powerful to be extractedfrom the standard thin accretion disks or rapidly spinning black holessurrounded by standard thin disks. If the advection dominated accretion flows(ADAFs) are present in these AGNs, their bright optical continuum luminositycannot be produced by pure-ADAFs due to their low accretion rates and lowradiation efficiency, unless the ADAFs transit to standard thin disks at someradii $R_{\rm tr}$. If this is the case, we find that the dimensionlessaccretion rates as high as 0.05 and transition from ADAFs to standard thindisks at rather small radii around 20GM/c^2 are required to explain theirbright optical continuum emission. We propose that the disk-corona structure ispresent at least in some AGNs in this sample. The plasmas in the corona arevery hot, and the pressure scale-height of the corona H\sim R. Powerful jetswith Q_jet \sim L_bol (bolometric luminosity) can form by the large-scalemagnetic fields created by dynamo processes in the disk corona of some AGNs.The maximal jet power extractable from the corona Q_jet^max\le 0.6L_c (L_c isthe corona luminosity) is expected by this jet formation scenario. Thestatistic results on the sample of AGNs are consistent with the predictions ofthis scenario. Finally, the possibility that the jet is driven from asuper-Keplerian rotating hot layer located between the corona and the cold diskis discussed. We find that, in principle, this layer can also produce apowerful jet with Q_jet\sim L_bol.Comment: 9 pages, accepted for publication in Ap