Evidence of a Long-Duration Component in the Prompt Emission of Short Gamma-Ray Bursts Detected with BeppoSAX

A statistical study on the light curves of all the short gamma-ray bursts (GRBs) detected with the Gamma Ray Burst Monitor (GRBM) aboard BeppoSAX is reported. Evidence of a very weak and long-duration component associated with these events in the two 1 s ratemeters of the GRBM (40-700 and >100 keV) is found. It starts a few tens of seconds before the burst and continues for about 30 s after the burst. The overall hardness of this component is comparable to that of the event itself. The detection of a signal before the onset time and the hardness are consistent with an interpretation of the long-duration component in terms of prompt emission associated with short GRBs.