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 \pm 0.05 ( chance probability of \sim 5.5 \times 10 ^ { -5 } ) between the spectral lag and the isotropic peak luminosity , L _ { iso } , with a best-fit power-law index of -1.2 \pm 0.2 , such that L _ { iso } \propto { lag } ^ { -1.2 } .
In addition , there is an anti-correlation between the source-frame spectral lag and the source-frame peak energy of the burst spectrum , E _ { pk } ( 1 + z ) .