2004ApJ...604..312G

Extremely powerful emission lines are observed in the X-ray afterglow of several gamma-ray bursts (GRBs). The energy contained in the illuminatingcontinuum that is responsible for the line production exceeds 10⁵¹ ergs, much higher than that of the collimated GRBs, constraining the models that might explain the production of X-ray emission lines. In this paper, we argue that this energy can come from a continuous postburst outflow. Focusing on a central engine of highly magnetized millisecond pulsar or magnetar, we find that the afterglow can be affected by the illuminating continuum, and therefore a distinct achromatic bump can be observed in the early afterglow light curves. With the luminosity of the continuous outflow that produces the line emission, we define the upper limit of the time when the bump feature appears. We argue that the reason why the achromatic bumps have not been detected so far is that the bumps appear at too early a time to be observed.