We present a systematic spectral analysis of 350 bright GRBs observed with BATSE, with high spectral and temporal resolution. Our sample was selected from the complete set of 2704 BATSE GRBs, and included 17 short GRBs. To obtain well-constrained spectral parameters, four different photon models were fitted and the spectral parameters that best represent each spectrum were statistically determined. A thorough analysis was performed on 350 time-integrated and 8459 time-resolved burst spectra. Using the results, we compared time-integrated and time-resolved spectral parameters, and also studied correlations among the parameters and their evolution within each burst. The resulting catalog is the most comprehensive study of spectral properties of GRB prompt emission to date, and provides constraints with exceptional statistics on particle acceleration and emission mechanisms in GRBs.

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Two short (<2 s) γ-ray bursts (GRBs) have recently been localized 1-4 and fading afterglow counterparts detected 2-4 . The combination of these two results left unclear the nature of the host galaxies of the bursts, because one was a starforming dwarf, while the other was probably an elliptical galaxy. Here we report the X-ray localization of a short burst (GRB 050724) with unusual γ-ray and X-ray properties. The X-ray afterglow lies off the centre of an elliptical galaxy at a redshift of z=0.258 (ref. 5), coincident with the position determined by groundbased optical and radio observations 6-8 . The low level of star formation typical for elliptical galaxies makes it unlikely that the burst originated in a supernova explosion. A supernova origin was also ruled out for GRB 050709 (ref. 3), even though that burst took place in a galaxy with current star formation. The isotropic energy for the short bursts is 2-3 orders of magnitude lower than that for the long