On the kinematic origin of the luminosity-pulse lag relationship in gamma-ray bursts

This Letter presents an interpretation based on gamma-ray burst source kinematics for the relationship found by Norris et al. between peak luminosity and energy-dependent pulse lag. I argue that the correlation should instead be between number luminosity and pulse lag. This interpretation improves the least-squares fit of this correlation for the known bursts by 25% or more. It also suggests a distance estimation scheme. I propose that this relationship is due to the variation in line-of-sight velocity among bursts. This interpretation allows one to speculate on the range of gamma-ray burst expansion velocities or the size of their jet opening angles.