Search for fast correlated X-ray and optical variability in Cir X-1 and XTE J1746-321

Search for fast correlated X-ray and optical variabilityin Cir X-1 and XTE J1746-321H.C. SpruitMax Planck Institute for Astrophysics, Box 1371, 85741 Garching, GermanyH. Steinle, G. KanbachMax Planck Institute for Extraterrestrial Physics,Box 1312, 85741 Garching, GermanyAbstractCoordinated observations X-ray+optical observations of two southern X-ray binaries, the black hole candidate XTE J1746-321 and the neutron staraccreter Cir X-1 (a ‘microquasar’) are reported. With a photon counting opticalphotometer on the 1.9m telescope at Sutherland, South Africa and the PCAdetector on RXTE, 4h each of simultaneous data were obtained on XTE J1746and Cir X-1. Cir X-1 showed no X-ray variability at the 2% level, XTE J1746was variable at 5-7% with a 5Hz QPO. Cross-correlation yielded no correlatedsignals on either source, to a level of 1%. A problem with a recently publishedorbital ephemeris of Cir X-1 is pointed out.