Redshift evolution of the lag relation for Swift GRBs
Azzam W.J., Eid H.A.
SourcetitleAIP Conference Proceedings
The lag relation for gamma-ray bursts (GRBs) is an anticorrelation between the time lag, ?, which represents the delay between the arrival of hard and soft photons, and the peak isotropic luminosity, Lp. In this study, we investigate the possible redshift evolution of this relation by using a sample of 31 Swift bursts taken from Ukwatta et al. (2010), who extracted the time-lags for all combinations of the Swift energy bands utilizing a modified cross-correlation method. Our analysis consists of binning the data in redshift, z, then applying a fit of the form: log(Lp) = A + Blog(?rest/<?rest>) for each bin, where ?rest is the time-lag in the burst's rest frame, and <?rest> is the corresponding mean value for the entire sample. The objective is to see whether the fitting parameters, A and B, evolve in a systematic way with z. Our results indicate that the normalization, A, does vary in a systematic way with redshift, whereas the slope, B, does not. However, it should be noted that although reasonable chi-square values were obtained, the data showed large scatter. � 2011 American Institute of Physics.