The Lag–Luminosity Relation in the GRB Source–Frame: An Investigation with Swift BAT Bursts

Spectral lag, which is defined as the difference in time of arrival of high and low energy photons, is a common feature in Gamma-ray Bursts (GRBs). Previous investigations have shown a correlation between this lag and the isotropic peak luminosity for long duration bursts. However, most of the previous investigations used lags extracted in the observer-frame only. In this work (based on a sample of 43 Swift long GRBs with known redshifts), we present an analysis of the lag-luminosity relation in the GRB source-frame. Our analysis indicates a higher degree of correlation −0.82±0.05 (chance probability of ∼ 5.5×10) between the spectral lag and the isotropic peak luminosity, Liso, with a best-fit power-law index of −1.2 ± 0.2, such that Liso ∝ lag. In addition, there is an anti-correlation between the source-frame spectral lag and the source-frame peak energy of the burst spectrum, Epk(1 + z).