Search for Fast Correlated X-ray and Optical Variability in Cir X-1 and Slx 1746-331

Coordinated observations X-ray+optical observations of two southern X-ray binaries, the black hole candidate SLX 1746-331 and the neutron star accreter Cir X-1 (a 'microquasar') are reported. With a photon counting optical pho-tometer on the 1.9m telescope at Sutherland, South Africa and the PCA detector on RXTE, 4h each of simultaneous data were obtained on SLX 1746 and Cir X-1. Cir X-1 showed no X-ray variability at the 2% level, SLX 1746 was variable at 5-7% with a 5Hz QPO. Cross-correlation yielded no correlated signals on either source, to a level of 1%.