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

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 \alpha~0.05-0.2. In particular, the slope is ~1.4 for the case of \alpha~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.