Speaker
Description
Some AGN are known to be efficient producers of strong, relativistic jets which power the extended radio sources. Largest and most powerful are the radio sources associated with AGN hosted by giant elliptical galaxies. Even among them, powerful jets are very rare phenomena and why this is so remains unanswered. Since relativistic jets are likely powered by rotating BHs via the Blandford-Znajek mechanism, the expected parameters deciding efficient jet production are BH spins and magnetic fluxes. If their values are large, the innermost portions of accretion flow should be affected by the jet production, which should be imprinted in their radiative properties. To verify this, we compare the radiative properties of radio-loud (RL) and radio-quiet (RQ) AGN selected from the Swift/BAT catalog with similar BH-masses and Eddington-ratios. We find that the only significant difference is the hard X-ray luminosities, which are about two times larger in RL-AGN than in RQ-AGN. This difference is speculated to come from RL-AGN having X-ray contribution from both the innermost, hot portions of the accretion flow and also a jet. However, this interpretation is challenged by our findings: (1) hard X-ray spectra of RL-AGN have similar slopes and high-energy breaks to those of RQ-AGN; (2) hard X-ray radiation is quasi-isotropic in both RL and RQ. We argue that the production of hard X-rays in RL is, like in the RQ, dominated by hot, central portions of accretion flows, while larger X-ray production efficiencies in RL-AGN can be associated with larger magnetic fields and faster-rotating BHs.
