Swift XRT Observations of X-ray Flares in GRB Afterglows
  The Swift XRT has been observing GRB afterglows since December 23, 2004. Three-quarters of these observations begin within 300 s of the burst onset, providing an unprecendented look at the behavior of X-ray emission from GRB afterglows in the first few hours after the burst. While most of the early afterglows have smoothly declining lightcurves, a substantial fraction has large X-ray flares on short time-scales. We suggest that these flares provide support for models with extended central engine activity producing late-time internal shocks. 
David N. Burrows, P. Romano, O. Godet, A. Falcone, C. Pagani, G.   Cusumano, S. Campana, G. Chincarini, J. E. Hill, P. Giomm...