Late-Time X-ray Flares during GRB Afterglows: Extended Internal Engine Activity. - Falcone, A. D.; Burrows, D. N.; Romano, P.; Kobayashi, S.; Lazzati, D.; Zhang, B.; Campana, S.; Chincarini, G.; Cusumano, G.; Gehrels, N.; Giommi, P.; Goad, M. R.; et al. (AIP Conference Proceedings, 2006)