The average Gamma-Ray Burst X-ray flaring activity

Gamma-ray burst (GRB) X-ray flares are believed to mark the late time activity of the central engine. I compute the temporal evolution of the average flare luminosity <L> in the common rest frame energy band of 44 GRBs taken from the large Swift 5-years data base. This work highlights the importance of a proper consideration of the threshold of detection of flares against the contemporaneous continuous X-ray emission. In the time interval 30 s<t<1000 s the flare luminosity decays as <L>~t^-2.7+/-0.1, while the flare isotropic energy decays as Eiso,flare~t^-1.7. These results are discussed in the context of GRB hyper-accretion models.