A unified accretion-ejection paradigm for black hole X-ray binaries

Abstract

We present a new picture for the central regions of Black Hole X-ray Binaries. In our view, these central regions have a multi-flow configuration which consists in (1) an outer standard accretion disc down to a transition radius rJ; (2) an inner magnetized accretion disc below rJ driving (3) a non relativistic self-collimated electron-proton jet surrounding, when adequate conditions for pair creation are met; (4) a ultra relativistic electron-positron beam. This accretion-ejection paradigm provides a simple explanation to the canonical spectral states, from radio to X/γ-rays, by varying the transition radius rJ and disc accretion rate independently. Large values of rJ correspond to the Quiescent state for low and the Hard state for larger . These states are characterized by the presence of a steady electron-proton MHD jet emitted by the disc below rJ. The hard X-ray component is expected to form at the jet basis. When rI becomes smaller than the marginally stable orbit ri, the whole disc resembles a standard accretion disc with no jet, characteristic of the Soft state. Intermediate states correspond to situations where . At large , an unsteady pair cascade process is triggered within the jet axis, giving birth to flares and ejection of relativistic pair blobs. This would correspond to the luminous intermediate state, sometimes referred to as the Very High state, with its associated superluminal motions. The variation of rJ independently of is a necessary ingredient in this picture. It arises from the presence of a large scale vertical magnetic field threading the disc. Features such as possible hysteresis and the presence of quasi-periodic oscillations would naturally fit within this new framework.