We present an updated catalog of 113 X-ray flares detected by Swift in the \sim 33 \% of the X-ray afterglows of Gamma-Ray Bursts ( GRB ) . 43 flares have a measured redshift .
For the first time the analysis is performed in 4 different X-ray energy bands , allowing us to constrain the evolution of the flare temporal properties with energy .
We find that flares are narrower at higher energies : their width follows a power-law relation w \propto E ^ { -0.5 } reminiscent of the prompt emission .
Flares are asymmetric structures , with a decay time which is twice the rise time on average .
Both time scales linearly evolve with time , giving rise to a constant rise-to-decay ratio : this implies that both time scales are stretched by the same factor .
As a consequence , the flare width linearly evolves with time to larger values : this is a key point that clearly distinguishes the flare from the GRB prompt emission .
The flare 0.3 - 10 keV peak luminosity decreases with time , following a power-law behaviour with large scatter : L _ { pk } \propto t _ { pk } ^ { -2.7 \pm 0.5 } .
When multiple flares are present , a global softening trend is established : each flare is on average softer than the previous one .
The 0.3 - 10 keV isotropic energy distribution is a log-normal peaked at 10 ^ { 51 } erg , with a possible excess at low energies .
The flare average spectral energy distribution ( SED ) is found to be a power-law with spectral energy index \beta \sim 1.1 .
These results confirmed that the flares are tightly linked to the prompt emission .
However , after considering various models we conclude that no model is currently able to account for the entire set of observations .