We propose to explain the recent observations of GRB early X-ray afterglows with SWIFT by the dissipation of energy in the reverse shock which crosses the ejecta as it is decelerated by the burst environment .
We compute the evolution of the dissipated power and discuss the possibility that a fraction of it can be radiated in the X-ray range .
We show that this reverse shock contribution behaves in a way very similar to the observed X-ray afterglows if the following two conditions are satisfied : ( i ) the Lorentz factor of the material which is ejected during the late stages of source activity decreases to small values \Gamma < 10 and ( ii ) a large part of the shock dissipated energy is transferred to a small fraction ( \zeta \mathrel { \hbox to 0.0 pt { \lower 3.0 pt \hbox { $ \mathchar 536 $ } \hss } \raise 2.0 % pt \hbox { $ \mathchar 316 $ } } 10 ^ { -2 } ) of the electron population .
We also discuss how our results may help to solve some puzzling problems raised by multiwavelength early afterglow observations such as the presence of chromatic breaks .