2006A&A...454..753L

The short/hard GRB 051210 was detected and located by the Swift-BAT instrument and rapidly pointed towards by the narrow field instruments. The XRT was able to observe a bright, rapidly fading X-ray emission. We present the analysis of the prompt and afterglow emission of this event. The BAT spectrum is a power-law with photon index 1.0±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)x10²⁰cm^–2. We find that the X-ray emission is consistent with the hypothesis that we are observing the curvature effect of a GRB that occurred in a low density medium, with no detectable afterglow attributable to an external shock. We estimate the density of the circumburst medium to be lower than 3x10^–3cm^–3. We also discuss different hypothesis on the possible origin of the flare.