D. Kopač, P. D'Avanzo, A. Melandri, S. Campana, A. Gomboc, J. Japelj, M. G. Bernardini, S. Covino, S. D. Vergani, R. Salvaterra, G. Tagliaferri
In this paper we present a sample of 11 short gamma-ray bursts (GRBs) with a robust redshift determination, discovered by the Swift satellite up to January 2011. We measure their X-ray absorbing column densities and collect data on the host galaxy offsets. We find evidence for intrinsic absorption and a weak correlation between the intrinsic absorbing column density and the projected offset of the GRB from its host galaxy center. This correlation becomes statistically more significant if we use the effective radius normalised host galaxy offsets instead. We find that the properties in the gamma regime (T90, fluence and 1-s peak photon flux) of short GRBs with "bright" and "faint" X-ray afterglow disfavour different prompt emission mechanisms, and that the (normalised) host galaxy offset and GRB duration (T90) do not correlate significantly. Finally, we examine the existence of short-lived and long-lived X-ray afterglows in short GRBs and find that some short GRBs with short-lived X-ray afterglows have their optical afterglow detected. This suggests that the X-ray afterglow duration does not seem to be a unique indicator of a specific progenitor and/or environment for short GRBs.
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http://arxiv.org/abs/1203.1864
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