Radio-X-ray correlation and the "quiescent state'' of black hole sources

Recently a correlation between the radio and X-ray luminosities is found, LR ∝ L 0.7 X , in black hole sources including black hole candidates in our galaxy and active galactic nuclei. We first attempt to understand the correlation in the context of an accretion-jet model developed for explaining the spectral and timing properties of XTE J1118+480. We find that this model can explain the observed correlation. More importantly, we show that when the X-ray luminosity is below a critical value, . 10–10LEdd, the correlation should turn and become steeper, LR ∝ L 1.23 X , and the X-ray radiation of the system should be dominated by the emission from the jet, rather than by the accretion flow. Possible observational evidence for our predictions is presented and future observations to further test our predictions are proposed. Subject headings: accretion, accretion disks — black hole physics — galaxies: active — ISM: jets and outflows — X-rays: stars