2006ApJ...645.1315P

The unique capability of the Swift satellite to perform a prompt and autonomous slew to a newly detected gamma-ray burst (GRB) has yielded the discovery of interesting new properties of GRB X-ray afterglows, such as the steep early light-curve decay and the frequent presence of flares detected up to a few hours after the GRB trigger. We present observations of GRB 050607, the fourth case of a GRB discovered by Swift with flares superimposed on the overall fading X-ray afterglow. The flares of GRB 050607 were not symmetric as in previously reported cases, showing a very steep rise and a shallower decay, similar to the fast rise, exponential decay that are frequently observed in the gamma-ray prompt emission. The brighter flare had a flux increase by a factor of ∼25, peaking for 30 s at a count rate of approximately 30 counts/s, and it presented hints of additional short-timescale activity during the decay phase. There is evidence of spectral evolution during the flares. In particular, at the onset of the flares the observed emission was harder, with a gradual softening as each flare decayed. The very short timescale and the spectral variability during the flaring activity are indicators of possible extended periods of energy emission by the GRB central engine. The flares were followed by a phase of shallow decay, during which the forward shock was being refreshed by a long-lived central engine or by shells of lower Lorentz factors, and by a steepening after approximately 12 ks to a decay slope considered typical of X-ray afterglows.