Multiwavelength variability of black hole x-ray binaries in the low/hard state

The behaviour of black hole X-ray binaries can be classified into five spectral states which are defined in terms of the X-ray spectral and timing properties of the source. These states show distinct and observable characteristics and transitions from one state to another often take place. Perhaps the most interesting of the five is the low/hard state; in theis state the X-ray emission appears to be confined to a Comptonising corona surrounding the black hole, the optical and infrared emission comes from a cold accretion disc with a large inner disc radius and a weak continuious jet is emitted from the central regions of the disc. In this thesis I study three black hole candidates which show low/hard state behaviour either most of the time (Cygnus X-1), quasi-periodically (LMC X-3) or intermittently (GS 1351-64). Observations were taken at X-ray, radio and optical wavelengths in order to study the preoperties of the low/hard state and the relationship between the accretion disc and the jet.