Context : The short/hard GRB051210 was detected and located by the Swift -BAT instrument and rapidly pointed towards by the narrow field instrumens .
The XRT was able to observe a bright X-ray afterglow , one of the few ever observed for this class of bursts .

Aims : We present the analysis of the prompt and afterglow emission of this event

Methods : The BAT spectrum is a power-law with photon index 1.0 \pm 0.3 .
The X-ray light curve decays with slope -2.58 \pm 0.11 and shows a small flare in the early phases .
The spectrum can be described with a power law with photon index 1.54 \pm 0.16 and absorption ( 7.5 _ { -3.2 } ^ { +4.3 } ) \times 10 ^ { 20 } cm ^ { -2 }

Results : We find that the X-ray emission is consistent with the hypothesis that we are observing the curvature effect of a GRB occurred in a low density medium , with no detectable afterglow .
We estimate the density of the circumburst medium to be lower than 4 \times 10 ^ { -3 } cm ^ { -3 } .
We also discuss different hypothesis on the possible origin of the flare .

Conclusions :