Modelling the `outliers' track of the radio--X-ray correlation in X-ray binaries based on disc-corona model

Abstract

The universal radio--X-ray correlation (F_R \propto F_X^{b}, b~0.5-0.7) has been found for a sample of black-hole X-ray binaries (BHBs) in their low/hard states, which can roughly be explained by the coupled model of jet and radiatively inefficient advection dominated accretion flow. However, more and more `outliers' were found in last few years, which evidently deviate from the universal radio-X-ray correlation and usually show a much steeper correlation with an index of ~1.4. Based on simple physical assumptions, the radiatively efficient accretion flows are speculated to exist in these `outliers'. In this work, we test this issue by modelling the `outliers' track based on the radiatively efficient disc-corona model and the hybrid jet model. We find that our model predicts a steeper radio--X-ray correlation with slopes >~1.2 for the typical viscosity parameter of α~0.05-0.2. In particular, the slope is ~1.4 for the case of α~0.1, which is consistent with the observational results of H1743-322 very well. Our results suggest that the `outliers' track may be regulated by the disc-corona model.