Jet-dominated advective systems: radio and X-ray luminosity dependence on the accretion rate

Abstract

We present a novel method to measure the accretion rate of radio emitting X-ray binaries (XRBs) and active galactic nuclei (AGN) independently of the X-ray luminosity. The radio emission of the jet is used as a tracer for the accretion rate and is normalised using sources of known accretion rates: island state neutron stars and efficiently radiating black holes close to a state transition. We show that the radio power in black holes and neutron stars is comparable for a given mass accretion rate and verify empirically the assumed analytic scaling of the radio luminosity with accretion rate. As our accretion measure is independent of the X-ray luminosities, we can search for radiatively inefficient accretion in black holes by comparing the X-ray luminosities with the accretion rate in XRBs and AGN. While the X-ray luminosity of efficiently radiating objects scales linearly with accretion rate, the scaling of hard state black holes is quadratical, in agreement with theoretical models. We show that the turnover from the inefficient quadratic scaling to the linear scaling has to occur at accretion rates of 1-10 % Eddington both in XRBs and AGN. The comparison of both accretion states supports the idea that in a black hole in the hard state some accretion power is advected into the black hole while the jet power exceeds the X-ray luminosity: these are therefore jet-dominated advective systems.