It is shown that in the duration-hardness plane the GRBs of the third intermediate subgroup are well defined. Their durations are intermediate (i.e. roughly between 2 and 10 seconds), but their hardnesses are the lowest. They are even softer than the long bursts.
@article{arxiv.astro-ph/0507688,
title = {Where is the 3rd subgroup of GRBs?},
author = {I. Horvath and A. Meszaros and L. G. Balazs and Z. Bagoly},
journal= {arXiv preprint arXiv:astro-ph/0507688},
year = {2007}
}