1997/11/25 by D. J. Crary, M. H. Finger, C. Kouveliotou +4 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Flux (metallurgy) #Fourier analysis #Fourier transform #Lag #Logarithm #Nyquist–Shannon sampling theorem #Spectral line #astro-ph
paper · pdf · doi:10.1086/311129
To appear in Astrophysical Journal Letters
arxiv created 1997/11/25 · openalex publication_date 1998/02/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
We have used the Fourier cross spectra of Cygnus X-1, as obtained with BATSE during a period of almost 2000 days, to estimate the phase (or time) lags between X-ray flux variations in the 20-50 and 50-100 keV bands as a function of Fourier frequency, ν. We find that these lag spectra do not depend on source state, as measured by the fractional rms variations of the X-ray flux. For frequencies well below the Nyquist frequency the variations in the 50-100 keV band lag those in the 20-50 keV band by a time interval τ∝ν −0.8 . Binning effects cause the observed hard X-ray time lags to decrease to 0 at the Nyquist frequency. Some previous results on time lags were affected by these binning effects. At photon energies above 10 keV, the time lags are approximately proportional to the logarithm of the ratio the energies of the passbands used.