A unified accretion–ejection paradigm for Black Hole X-ray binaries Original Research Article

We present a unified accretion–ejection picture that explains the different spectral state of Black Hole X-ray binaries (BHXrB) from radio to X/γ-rays. In this view, the central region of BHXrB has a multi-flow configuration which consists in (1) an outer standard accretion disc, (2) an inner magnetized accretion disc driving, (3) a self-collimated electron–proton MHD jet, surrounding and (4) a relativistic electron–positron beam when adequate conditions are met. This picture provides a simple and unified explanation to the various canonical spectral states of BH X-ray binaries, by varying the transition radius rJ between the inner disc driving jets and the outer standard disc. In this framework, large rJ correspond to Quiescent and Hard states while small rJ correspond to Thermal Dominant ones. In between these two extremes, rJ can reach values that switches on the pair cascade process giving birth to a relativistic electron–positron beam. This would correspond to the bright intermediate state.