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 obtai ned from PCA./RXTE observation. By superposing many shots lined up at the p eak, a mean profile was obtained, and this was done separately for the diff erent states, high, transitional and low. The mean shot profile is differen t for the different states. The duration of shot is shorter in the high tha n in the transitional state. In both, the duration is about 0.11 s, which i s shorter than in the low state. The profile is more asymmetrical in high t han in low energy bands. In the transitional state, the average hardness du ring shots is lower than that of the steady component. The mechanism of sho t generation is discussed.