Quenched millimetre emission from Cygnus X-1 in a soft X-ray state

We present millimetre wavelength observations of the black hole candidate X-ray binary Cygnus X-1 that indicate a suppression, or quenching, of the emission as the source switches to a softer X-ray state. Combining the data with those for another black hole candidate, XTE J1118+480, we demonstrate that the millimetre emission shows the same coupling to X-rays as the radio emission, although with a much stronger sensitivity to spectral shape. We therefore confirm the association of the millimetre emission with the jets in low-hard state black hole candidate X-ray binaries.