  The Swift X-ray Telescope (XRT) has discovered that flares are quite common
in early X-ray afterglows of Gamma-Ray Bursts (GRBs), being observed in roughly
50% of afterglows with prompt followup observations. The flares range in
fluence from a few percent to ~ 100% of the fluence of the prompt emission (the
GRB). Repetitive flares are seen, with more than 4 successive flares detected
by the XRT in some afterglows. The rise and fall times of the flares are
typically considerably smaller than the time since the burst. These
characteristics suggest that the flares are related to the prompt emission
mechanism, but at lower photon energies. We conclude that the most likely cause
of these flares is late-time activity of the GRB central engine.
