Spectral lags and the lag-luminosity relation: An investigation with swift bat gamma-ray bursts

Abstract

Spectral lag, the time difference between the arrival of high-energy and low-energy photons, is a common feature in gamma-ray bursts (GRBs). Norris etal. reported a correlation between the spectral lag and the isotropic peak luminosity of GRBs based on a limited sample. More recently, a number of authors have provided further support for this correlation using arbitrary energy bands of various instruments. In this paper, we report on a systematic extraction of spectral lags based on the largest Swift sample to date of 31GRBs with measured redshifts. We extracted the spectral lags for all combinations of the standard Swift hard X-ray energy bands: 15-25keV, 25-50keV, 50-100keV, and 100-200keV and plotted the time dilation corrected lag as a function of isotropic peak luminosity. The mean value of the correlation coefficient for various channel combinations is -0.68 with a chance probability of ∼0.7 × 10 -3. In addition, the mean value of the power-law index is 1.4 ± 0.3. Hence, our study lends support to the existence of a lag-luminosity correlation, albeit with large scatter. © 2010. The American Astronomical Society.