Spectral Diagnostics of Blazar Central Engines. II. Hydromagnetic Theory

Abstract

This article presents hydromagnetic theory that is capable of explaining the fundamental physics responsible for correlations between spectral shape in the radio to submillimeter band with other observ- able characteristics of core-dominated radio sources presented in a companion paper. The basic model consists of a rotating black hole surrounded by an accretion disk. Large-scale magnetic Nux threads the accretion disk, the event horizon of the black hole, and the ergospheric gap in between. It is concluded that there are two dominant components, the ergospheric diskEdriven wind and the horizon magnetosphereEdriven wind. For the -rst time, all three potential magnetized plasma wind generation regions are studied in unison instead of in isolation. This drastically changes oneIs interpretation of the achievable energy Nux driven by a particular power source. A key new result is that quite generally, the accretion diskEdriven wind is much weaker than the ergosphere-driven wind in powerful radio sources. The ergospheric diskEdriven wind is by far the most powerful energy source associated with rapidly rotating black holes. It is argued to be prominent in quasars, and it is the primary conduit of energy for the VLBI jet and the large-scale radio emission in these sources. The horizon magnetospheric wind is associated with blazar activity and c-ray emission. In the theory, BL Lac objects contain slow II rotat- ing black holes in general and have a weak ergospheric diskEdriven wind. Thus, the horizon magnetosphereEdriven wind is prominent in BL Lac objects in both the VLBI jet and the unresolved core. This two-component model not only explains the spectral correlations found in the companion paper, but it predicts evolutionary e†ects in extragalactic radio sources that agree with observation, including evolution in the 3CR catalog of radio sources, and the redshift distribution of BL Lac objects and quasars. It also presents plausible explanations of the maximum intrinsic luminosities detected in FR II radio sources as well as FR I radio sources. Subject headings: black hole physics E galaxies: jets E galaxies: nuclei E MHD