5 Conclusions

1.

It is possible that the fit using three log-normal functions is accidental, and that there are only two types of GRBs. However, if the T₉₀ distribution of these two types of GRBs is log-normal, then the probability that the third group of GRBs is an accidental fluctuation is less than 0.5%.

2.

Therefore, the statistics indicate that the third component is present. However, the physical existence of the third group is still argueable. The sky distribution of the third component is anisotropic as proven by Balázs et al. (1998), Balázs et al. (1999), Mészáros et al. (2000), Litvin et al. (2001). The $\log N{-}\log S$ distribution may also differ from the other group's distributions (Horváth 1998). Alternatively Hakkila et al. (2000c) believe the third statistically proved subgroup is only a deviation caused by a complicated instrumental effect, which can reduce some faint long burst durations. This paper does not deal with this particular effect, however systematic triggering effects were examined and after that the third group was still statistically significant.

3.

Therefore, this theme should be discussed in future papers to further elucidate the reality and properties of the third class.

Acknowledgements

This research was supported in part through NATO advanced research fellowship 1037/NATO/01, OTKA F029461, OTKA T034549. Useful discussions with L. G. Balázs, J. T. Bonnell, E. Fenimore, J. Hakkila, A. Mészáros, P. Mészáros, are appreciated. The author also thanks B. McBreen, the referee, for useful comments that improved the paper.