SIMBAD references

We carried out a systematic search of precursors on the sample of short gamma-ray bursts (GRBs) observed by Swift. We found that ∼8%-10% of short GRBs display such early episodes of emission. One burst (GRB 090510) shows two precursor events, the former ∼13 s and the latter ∼0.5 s before the GRB. We did not find any substantial difference between the precursor and the main GRB emission, and between short GRBs with and without precursors. We discuss possible mechanisms to reproduce the observed precursor emission within the scenario of compact object mergers. The implications of our results on quantum gravity constraints are also discussed.