Millisecond temporal structure in Cygnus X-1

Evidence is presented for the X-ray variability of Cyg X-1 on time scales down to 1 ms. Several "bursts" of millisecond duration are observed. The duty cycle for bursting is estimated to be >2 X 1 averaged over the entire 49-s exposure, although the maximum burst activity is associated with a region of enhanced emission lasting about s. Such bursts may be associated with turbulence in disk accretion at the innermost orbits for a black hole. Sitbject headings: black holes - X-rays