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. We present the analysis of the prompt and afterglow emission of this
event The BAT spectrum is a power-law with photon index 1.1 +/-0.3. The X-ray
light curve decays with slope 2.58+/-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+/-0.16 and absorption (7.5 (-3.2, +4.3)*10^20 cm-2 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*10^-3
cm^-3. We also discuss different hypothesis on the possible origin of the
flare.Comment: 5 pages, 3 figures, submitted to A&A Letter
