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 ave...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.展开更多
基金supported by the National Basic Research Program of China (Grant No. 2009CB824800)the National Natural Science Foundation of China (Grant No. 10533020)
文摘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.
