Annual Fall Meeting and 82nd General Assembly of the Astronomische Gesellschaft

Potsdam, Germany
2009 September 21–25

Long-term timing analysis of the black hole binary Cygnus X-1

S. Pirner, K. Pottschmidt, M. Böck, M. Hanke, J. Wilms, V. Grinberg, S. Markoff, M. Nowak, G. Pooley

The accreting X-ray binary Cygnus X-1 has been target of our biweekly monitoring campaign with the Rossi X-Ray Timing Explorer (RXTE) for more than ten years. We present the long-term timing analysis of Cygnus X-1 in the 2-70 keV band based on this database with more than 1200 spectra and lightcurves with 2 ms time resolution. The monitoring covers the changes in this accreting system in unprecedented detail. Power spectra (PSD) are calculated for every RXTE orbit (∼90 min). In the spectral hard state, in which Cygnus X-1 is found most of the time, the power spectra in the 0.003-128 Hz range can be described with two to four broad Lorentzian noise components. The peak frequency and strength of these broad-noise components are strongly correlated with the spectral parameters of the source and therefore likely associated with the accretion disk corona. After a transition to the soft state in which the X-ray spectrum is dominated by thermal radiation from the accretion disk, the shape of the power spectrum changes and the broad noise components vanish. The increase of the time lags between light curves at higher and lower energies from the hard towards the transition is a further indicator of the changes in the accretion geometry. Simultaneous radio monitoring with the Ryle Telescope reveals correlations between radio and X-ray emission processes.