ON THE ROLE OF THE ACCRETION DISK IN BLACK HOLE DISK–JET CONNECTIONS

Abstract

Models of jet production in black hole systems suggest that the properties of the accretion disk—such as its mass accretion rate, inner radius, and emergent magnetic field—should drive and modulate the production of relativistic jets. Stellar-mass black holes in the "low/hard" state are an excellent laboratory in which to study disk–jet connections, but few coordinated observations are made using spectrometers that can incisively probe the inner disk. We report on a series of 20 Suzaku observations of Cygnus X-1 made in the jet-producing low/hard state. Contemporaneous radio monitoring was done using the Arcminute MicroKelvin Array radio telescope. Two important and simple results are obtained: (1) the jet (as traced by radio flux) does not appear to be modulated by changes in the inner radius of the accretion disk and (2) the jet is sensitive to disk properties, including its flux, temperature, and ionization. Some more complex results may reveal aspects of a coupled disk–corona–jet system. A positive correlation between the reflected X-ray flux and radio flux may represent specific support for a plasma ejection model of the corona, wherein the base of a jet produces hard X-ray emission. Within the framework of the plasma ejection model, the spectra suggest a jet base with v/c ≃ 0.3 or the escape velocity for a vertical height of z ≃ 20 GM/c² above the black hole. The detailed results of X-ray disk continuum and reflection modeling also suggest a height of z ≃ 20 GM/c² for hard X-ray production above a black hole, with a spin in the range 0.6 ⩽ a ⩽ 0.99. This height agrees with X-ray time lags recently found in Cygnus X-1. The overall picture that emerges from this study is broadly consistent with some jet-focused models for black hole spectral energy distributions in which a relativistic plasma is accelerated at z = 10–100 GM/c². We discuss these results in the context of disk–jet connections across the black hole mass scale.