The Giant X‐Ray Flare of GRB 050502B: Evidence for Late‐Time Internal Engine Activity

Until recently, X-ray flares during the afterglow of gamma ray bursts (GRBs)were a rarely detected phenomenon, thus their nature is unclear. During theafterglow of GRB 050502B, the largest X-ray flare ever recorded rose rapidlyabove the afterglow lightcurve detected by the Swift X-ray Telescope. The peakflux of the flare was >500 times that of the underlying afterglow, and itoccurred at >12 minutes after the nominal prompt burst emission. The fluence ofthis X-ray flare, (1.0 +/- 0.05) x 10^{-6} erg cm^{-2} in the 0.2-10.0 keVenergy band, exceeded the fluence of the nominal prompt burst. The spectraduring the flare were significantly harder than those measured before and afterthe flare. Later in time, there were additional flux increases detected abovethe underlying afterglow, as well as a break in the afterglow lightcurve. Allevidence presented below, including spectral and particularly timinginformation during and around the giant flare, suggests that this giant flarewas the result of internal dissipation of energy due to late central engineactivity, rather than an afterglow-related effect. We also find that the dataare consistent with a second central engine activity episode, in which theejecta is moving slower than that of the initial episode, causing the giantflare and then proceeding to overtake and refresh the afterglow shock, thuscausing additional activity at even later times in the lightcurve.Comment: accepted for publication in Ap