Search for fast correlated X-ray and optical variability in Cir X-1 and   XTE J1746-321
  Coordinated observations X-ray+optical observations of two southern X-ray binaries, the black hole candidate XTE J1746-321 and the neutron star accreter Cir X-1 (a `microquasar') are reported. With a photon counting optical photometer on the 1.9m telescope at Sutherland, South Africa and the PCA detector on RXTE, 4h each of simultaneous data were obtained on XTE J1746 and Cir X-1. Cir X-1 showed no X-ray variability at the 2% level, XTE J1746 was variable at 5-7% with a 5Hz QPO. Cross-correlation yielded no correlated signals on either source, to a level of 1%. A problem with a recently published orbital ephemeris of Cir X-1 is pointed out. 
H.C. Spruit, H. Steinle, G. Kanbach