2012ApJ...753...24L

Giant X-ray cavities lie in some active galactic nuclei (AGNs) locating in central galaxies of clusters, which are estimated to have stored 10⁵⁵-10⁶² erg of energy. Most of these cavities are thought to be inflated by jets of AGNs on a timescale of ≳ 10⁷ years. The jets can be either powered by rotating black holes or the accretion disks surrounding black holes, or both. The observations of giant X-ray cavities can therefore be used to constrain jet formation mechanisms. In this work, we choose the most energetic cavity, MS 0735+7421, with stored energy ∼10⁶² erg, to constrain the jet formation mechanisms and the evolution of the central massive black hole in this source. The bolometric luminosity of the AGN in this cavity is ∼10^–5 L_Edd, however, the mean power of the jet required to inflate the cavity is estimated as ∼0.02L_Edd, which implies that the source has previously experienced strong outbursts. During outbursts, the jet power and the mass accretion rate should be significantly higher than its present values. We construct an accretion disk model in which the angular momentum and energy carried away by jets are properly included to calculate the spin and mass evolution of the massive black hole. In our calculations, different jet formation mechanisms are employed, and we find that the jets generated with the Blandford-Znajek (BZ) mechanism are unable to produce the giant cavity with ∼10⁶² erg in this source. Only the jets accelerated with a combination of the Blandford-Payne and BZ mechanisms can successfully inflate such a giant cavity if the magnetic pressure is close to equipartition with the total (radiation+gas) pressure of the accretion disk. For a dynamo-generated magnetic field in the disk, such an energetic giant cavity can be inflated by the magnetically driven jets only if the initial black hole spin parameter a₀ ≳ 0.95. Our calculations show that the final spin parameter a of the black hole is always ∼0.9-0.998 for all the computational examples that can provide sufficient energy for the cavity of MS 0735+7421.