Shot Cutoff Timescales in Different Spectral States of Cygnus X-1

We investigate the shot cutoff timescale evolutions during different spectralstates in the black hole binary Cygnus X-1 with the recently proposed wspectral analysis technique. For low energy shots, their cutoff timescaledecreases from the low state to intermediate state, and to high statemonotonically. However in the high energy range, where shots are believed to bereprocessed in the hot corona, timescales are almost the same for differentspectral states. A linear correlation is found between the energy spectrumphoton index and the shot cutoff timescale at low energies. Both narrow andbroad iron Kalpha lines are distinguished from timing analysis, providingdynamical evidence that broad and narrow iron lines originate respectively atsmall and large radii of the accretion disk. Possible mechanisms for statetransitions and accretion flow geometry in accreting stellar mass black holesare discussed.Comment: accepted for publication in ApJ