In this chapter the algorithms developed the GRB search and the GRBM data used for this search are described in detail.
A brief description of the GRBM data is given at the beginning of this chapter: in particular, the main sources of modulation in the detector background, like those connected with the Earth magnetic field variations along the orbit, are mentioned: actually, these background modulations strongly constrain the GRB quest parameters, as for the background fit.
Two different kinds of search algorithms are discussed: the early SoftWare Trigger Conditions (SWTCs) and the late SWTCs: benefits and drawbacks of both kinds are examined.
We also distinguish between two kinds of GRB search, i.e. on- and off-line: the first deals with the GRBM RAW data, which are temporarily archived orbit by orbit and maintain a provisional character, while the second deals with archive data (FOT, hereafter, to distinguish from RAW). Although the search algorithms are basically the same in both cases, the parameters defining them are slightly different: the motivations of this choice are discussed. The main features of the two GRB quests are the central topics of the next chapter.
Thanks to a more reliable background fit automatically performed, only the late SWTCs have been applied to the on-line quest. Nevertheless, both classes of search algorithms contributed to build the GRB catalog, thanks to their different search capabilities.
Some examples of bursts that did not trigger the on-board logic, but were identified by the SWTCs, are shown as well.
Eventually, among the late SWTCs there is one, acting as threshold on the spectral hardness of the GRB candidates, i.e. the Hardness Ratio SWTC, that deserves particular attention, since it turned out to be very effective in discarding the majority of false events, that mimic GRBs. The main spectral differences between GRBs and other events, like spikes due to high-energy particles crossing the detectors, or solar X-ray flares, are discussed.