Comprehensive Analysis of RXTE Data from Cyg X-1: Spectral Index-Quasi-Periodic Oscillation Frequency-Luminosity Correlations

摘要

We present timing and spectral analysis of ~ 2.2 Ms of RXTE archival datafrom Cyg X-1. Using a generic Comptonization model we reveal that the spectrumof Cyg X-1 consists of three components: a thermal seed photon spectrum, aComptonized part of the seed photon spectrum and the iron line. We find astrong correlation between the 0.1-20 Hz frequencies of quasiperiodicoscillations (QPOs) and the spectral index. Presence of two spectral phases(states) are clearly seen in the data when the spectral indices saturate at lowand high values of QPO frequencies. This saturation effect was discoveredearlier in a number of black hole candidate (BHC) sources and now we stronglyconfirm this phenomenon in Cyg X-1. In the soft state this index-QPO frequencycorrelation shows a saturation of the photon index Gamma ~ 2.1 at high valuesof the low frequency u_{L}. The saturation level of Gamma~ 2.1 is the lowestvalue found yet in BHCs. The bolometric luminosity does not show clearcorrelation with the index. We also show that Fe K_{lpha} emission linestrength (equivalent width, EW) correlates with the QPO frequency. The EWincreases from 200 eV in the low/hard state to 1.5 keV in the high/soft state.The observational correlations revealed compel us to propose a scenario for thespectral transition and iron line formation which occur in BHC sources. We alsopresent the spectral state (power-law index) evolution for eight years of CygX-1 observations by RXTE.