1 Introduction

Since the discovery of the GRB (gamma-ray burst) phenomenon, about thirty years ago, the possible correlations among the known physical parameters of GRBs have been studied by several authors (Golenetskii et al. 1983; Barat et al. 1984; Belli 1984, 1993, etc.) and more recently by Mallozzi et al. (1995); Dezalay et al. (1997) etc. Some correlations have been put in evidence, e.g. rise-time and decay-time, rise-time and spectral hardness, and, the most important one, intensity - spectral hardness. But the lack of bursts allowed only fragmentary results. At present the available number of bursts is higher, due to the data provided by very powerful experiments like the BATSE experiment, on board of the US CGRO satellite, the French-Soviet PHEBUS satellites, the Japanese satellites as GINGA, ASCA etc. We use for this analysis the 1840 events of the 4B BATSE catalog. Not all the physical parameters provided by the catalog are available for all the events. We will specify every time the number of the events used in each reported analysis.