The temporal and spectral analysis of 9 bright X-ray flares out of a sample of 113 flares observed by Swift reveals that the flare phenomenology is strictly analogous to the prompt \gamma -ray emission : high energy flare profiles rise faster , decay faster and peak before the low energy emission .
However , flares and prompt pulses differ in one crucial aspect : flares evolve with time .
As time proceeds flares become wider , with larger peak lag , lower luminosities and softer emission .
The flare spectral peak energy E _ { p,i } evolves to lower values following an exponential decay which tracks the decay of the flare flux .
The two flares with best statistics show higher than expected isotropic energy E _ { iso } and peak luminosity L _ { p,iso } when compared to the E _ { p,i } - E _ { iso } and E _ { p,i } - L _ { iso } prompt correlations . E _ { p,i } is found to correlate with L _ { iso } within single flares , giving rise to a time resolved E _ { p,i } ( t ) - L _ { iso } ( t ) .
Like prompt pulses , flares define a lag-luminosity relation : L _ { p,iso } ^ { 0.3 - 10 keV } \propto t _ { lag } ^ { -0.95 \pm 0.23 } .
The lag-luminosity is proven to be a fundamental law extending \sim 5 decades in time and \sim 5 in energy .
Moreover , this is direct evidence that GRB X-ray flares and prompt gamma-ray pulses are produced by the same mechanism .
Finally we establish a flare- afterglow morphology connection : flares are preferentially detected superimposed to one-break or canonical X-ray afterglows .