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2014MNRAS.440..965H - Mon. Not. R. Astron. Soc., 440, 965-970 (2014/May-2)

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

HUANG C.-Y., WU Q. and WANG D.-X.

Abstract (from CDS):

A universal radio-X-ray correlation (F_R∝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. This can roughly be explained by a coupled model of a jet and radiatively inefficient advection-dominated accretion flow. However, more and more outliers' have been found in the 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, it is speculated that radiatively efficient accretion flows occur in these outliers. In this work, we test this hypothesis 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 typical viscosity values of α ∼ 0.05-0.2. In particular, the slope is ∼ 1.4 for the case α ∼ 0.1, which is consistent with observational results for H1743-322. Our results suggest that the outliers track might be regulated by the disc-corona model.