http://arxiv.org/abs/1509.02598
Two types of correlations between the radio and X-ray luminosities ($L_R$ and $L_X$) of black hole sources has been found. For the traditional type of sources, the correlation can be described by a single power-law. For the other type of sources, while the correlation can still be described by power-law forms, it consists three branches according to the X-ray luminosity, with different power-law indexes. In this paper, we try to explain these correlations in the framework of the coupled accretion-jet model. We attribute the difference between these two types of sources to the difference in the value of viscous parameter $\alpha$. For the “single power-law” sources, their $\alpha$ is high; so their accretion is always in the mode of ADAF (advection-dominated accretion flow) for the whole range of X-ray luminosity. For those “hybrid power-law” sources, the value of $\alpha$ is small so their accretion modes change from ADAF to LHAF (luminous hot accretion flow) to two-phase accretion as the accretion rate increases. Because the radiative efficiency of the hot accretion flow on the mass accretion rate is different for these three accretion modes, they will lead to different power-law indexes in the $L_R$ — $L_X$ correlation. The reason of the different $\alpha$ may be because of the different configuration of magnetic field in the accretion material coming from the companion stars. Constraints on the ratio of the mass lost rate into the jet and the mass accretion rate in the accretion flow have been obtained, which can be tested in future by radiative magnetohydrodynamic (MHD) numerical simulations on jet formation.
F. Xie and F. Yuan
Thu, 10 Sep 15
13/67
Comments: 7 pages, 2 figures. Submitted to MNRAS. Comments are welcome
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