Tsing Hua Univ, Dept Engn Phys, Beijing 100084, Peoples R China
; Tsing Hua Univ, Ctr Astrophys, Beijing 100084, Peoples R China
; Tsing Hua Univ, Dept Phys, Beijing 100084, Peoples R China
; Univ Alabama, Dept Phys, Huntsville, AL 35899 USA
; Chinese Acad Sci, Inst High Energy Phys, Lab Particle Astrophys, Beijing 100039, Peoples R China
; NASA, Space Sci Lab, George C Marshall Space Flight Ctr, Huntsville, AL 35812 USA
We investigate the shot cutoff timescale evolutions during different spectral states in the black hole binary Cygnus X-1 with the recently proposed w spectral analysis technique. For low-energy shots, their cutoff timescale decreases from the low state to the intermediate state and to the high state monotonically. However, in the high-energy range, where shots are believed to be reprocessed in the hot corona, timescales are almost the same for different spectral states. A linear correlation is found between the energy spectrum photon index and the shot cutoff timescale at low energies. Both narrow and broad iron Kalpha lines are distinguished from timing analysis, providing dynamical evidence that broad and narrow iron lines originate, respectively, at small and large radii of the accretion disk. Possible mechanisms for state transitions and accretion flow geometry in accreting stellar mass black holes are discussed.