Spectral Lags Obtained by CCF of Smoothed Lightcurves

TL;DR

This paper introduces a new method for calculating spectral lags in gamma-ray bursts using smoothed light curves and cross-correlation, improving accuracy and revealing lag distributions and evolution.

Contribution

The paper presents a novel technique employing Loess smoothing and direct CCF maximization to measure spectral lags, reducing manual fitting errors and enabling detailed analysis.

Findings

Spectral lag distribution fits four Gaussian components.

Confirmed anti-correlation between spectral lag and luminosity.

Observed spectral lag evolution in multi-peak GRBs.

Abstract

We 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 BAT/Swift gamma-ray bursts with known redshifts, and confirmed the anti-correlation between the spectral lag and the isotropy 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 multi-peak GRBs seem to evolve with time.