Early Afterglow and Variability

We show that simple kinematic arguments can give limits on variabilities in gamma‐ray burst (GRB) afterglows. These limits are violated by X‐ray flares in the early afterglows recently identified by the Swift satellite. We discuss that a probable solution is that the central engine continues to eject an intermittent outflow for a very long timescale up to 1 day. This long‐lived engine model may also explain the flat decay of early X‐ray afterglows, while the gamma‐ray efficiency of GRBs should be incredibly high (>75–90%) in this model. We suggest new possible models to evade this efficiency crisis and discuss implications for future observations.