Quiescent Burst Evidence for Two Distinct Gamma-Ray Burst Emission Components

摘要

We have identified two quiescent gamma-ray bursts (GRBs) (bursts having two or more widely separated distinct emission episodes) in which the postquiescent emission exhibits distinctly different characteristics than the prequiescent emission. In these two cases (BATSE GRBs 960530 and 980125), the second emission episode has a longer lag, smoother morphology, and softer spectral evolution than the first episode. Although the prequiescent emission satisfies the standard internal shock paradigm, we demonstrate that the postquiescent emission is more consistent with external shocks. We infer that some observed soft, faint, long-lag GRBs are external shocks in which the internal shock signature is not observed. We further note that the peak luminosity ratio between quiescent episodes is not in agreement with the ratio predicated by the lag versus peak luminosity relationship. We briefly discuss these observations in terms of current collapsar jet models.