2 Quick-look sub-second GRB analysis

  

Figure 1: Illustration of the necessity for the analysis of high-time resolution data in order to discriminate true bursts from background events. Both light curves are of the sub-second burst GRB 961122. On the left: PDS lateral shield ratemeter of 1 s resolution (4 minutes centered on trigger time). On the right: GRBM data of 8 ms resolution (8 seconds around trigger time)

The BeppoSAX SOC GRB procedure relies on the presence of a trigger, either from the GRBM or from BATSE, which contains the approximate time of a possible GRB. Given a trigger, the initial step in the procedure involves the analysis of the scientific housekeeping data of the Phoswich Detector System (PDS) lateral shields. These ratemeter data are inspected primarily in order to ascertain the validity of the trigger. However, the maximum 1 s resolution of this data sets a similar lower limit to the GRB duration which can be effectively discriminated from the many background events or noise fluctuations. In order to extend the systematic quick-look detection of GRBs to the sub-second class of events, an analysis must be made at a higher temporal resolution (see Fig. 1). Indeed, in the BeppoSAX SOC sub-second bursts procedure an analysis of the high time resolution GRBM packets is foreseen with this aim in mind. The high time resolution packets contain lateral shield data with temporal resolution of up to 8 ms, and are created on board whenever the GRBM trigger condition is fulfilled.