X‐Ray Shots of Cygnus X‐1

Abstract

X-ray shots of Cyg X-1 in different energy bands and spectral states have been studied with proportional counter array (PCA)/Rossi X-Ray Timing Explorer (RXTE) observations. The detailed shot structure is obtained by superposing many shots with 1 ms time bin through aligning their peaks with an improved algorithm. In general, the shots are composed of a slow rise and fast decay. The shot structures in the different states are different. The duration of a shot in the high state is shorter than that in the low and transition states. The shot profile in the high-energy band is more asymmetric and narrower than that in the low-energy band. The average hardness of a shot is lower than that of steady emission in the transition and low states but higher than that in the high state. The time lags between the shots in higher and lower energy bands have been found in the different states. In transition states, the time lag is largest among the different states of Cyg X-1, and it is smallest in the low state. The implications of the observed shot features for shot models are discussed.