The short timescale bursts of Cyg X-1 in the high and transitional states

Short timescale bursts or "shots" of Cyg X-1 in one ms time bins were obtained from PCA./RXTE observation. By superposing many shots lined up at the peak, a mean profile was obtained, and this was done separately for the different states, high, transitional and low. The mean shot profile is different for the different states. The duration of shot is shorter in the high than in the transitional state. In both, the duration is about 0.11 s, which is shorter than in the low state. The profile is more asymmetrical in high than in low energy bands. In the transitional state, the average hardness during shots is lower than that of the steady component. The mechanism of shot generation is discussed.