2 The GRB sample

Table 1 shows the GRBs in our sample with some basic information about the WFC and GRBM data. T_x and $T_\gamma$ give the time duration of the primary event in the X-ray (2-26 keV) and $\gamma$-ray (40-700 keV) bands, respectively. Our sample includes almost all GRBs that triggered the GRBM until 25 April 1998, were detected with one of the two WFCs and were observed with the BeppoSAX NFIs. Peculiar GRBs are included in the sample, like GRB 970111, the afterglow emission of which was not firmly detected (Feroci et al. 1998).

The WFC and GRBM light curves of each GRB were divided into several temporal sections and, for each of them, the average spectrum in the 2-700 keV range was fitted with a Band's model (Band et al. 1993) photoelectrically absorbed by the interstellar medium along the GRB direction.

  

Table 1: GRBs included in our sample with WFC and GRBM data

^(a) Peak fluxes in units of 10^-7 erg cm^-2 s^-1.