Spectral Lags Obtained by CCF of Smoothed Light Curves

Abstract

ABSTRACTWe present a new technique to calculate the spectral lags of gamma-ray bursts (GRBs). Unlike previous processing methods, we first smooth the light curves of gamma-ray bursts in high- and low-energy bands using the “Loess” filter, then we directly define the spectral lags as such to maximize the cross-correlation function (CCF) between two smoothed light curves. This method is suitable for various shapes of CCF; it effectively avoids the errors caused by manual selections for the fitting function and fitting interval. Using the method, we have carefully measured the spectral lags of individual pulses contained in Swift BAT gamma-ray bursts with known redshifts and confirmed the anticorrelation between the spectral lag and the isotropic luminosity. The distribution of spectral lags can be well fitted by four Gaussian components, with the centroids at 0.03 s, 0.09 s, 0.15 s, and 0.21 s, respectively. We find that some spectral lags of the multipeak GRBs seem to evolve with time.