Calculating the time lags over different timescales using the cross-correlation technique may lead to a biased estimate of small timescales. Given a timescale for lightcurve binning, we propose to subtract the local average instead of the global average during the cross-correlation, in order to filter variations on timescales larger than the bin size. The new method allows us to make an unbiased estimate of the time lags using RXTE/PCA data on timescales as small as ∼5 ms, where the Fourier technique becomes invalid. We calculate the time lag spectra of Cygnus X-1 at different spectral states with the new method, and find that the source appears to have similar X-ray lags on small timescales independent of its spectral states.
相似文献We have analyzed International Gamma-Ray Astrophysics Laboratory (INTEGRAL) data corresponding to observations of the high mass X-ray binary (HMXB) V0332+53 during its huge outburst which occurred in 2004–2005, and found that there is a quasi periodic signal with ultra low frequency of roughly 4−5×10−5 Hz in the observation. This feature is revealed through a series of consistent analyses of imagings and fittings of the energy spectrum for each science window (SCW), and shows up in the corresponding light curves. The analysis of the power spectrum also provides a hint of a power peak located around 4×10−5 Hz, after subtracting off the linear trend of the light curve, and shows the consistency with the previous analyses. A similar feature shows up in our analysis of the light curve of Crab in hexagonal dithering mode. Therefore, an instrumental effect on the flux modulation might exist in the INTEGRAL data product of different levels: imaging, spectral fitting and light curve analysis, at least for the observational mode of hexagonal dithering. Such an effect is, to our knowledge, not yet available in the current literature.
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