Gamma-ray bursts spectral correlations and their cosmological use

The correlations involving the long-GRB prompt emission energy represent a new key to understand the GRB physics. These correlations have been proved to be the tool which makes long-GRBs a new class of standard candles. Gamma Ray Bursts, being very powerful cosmological sources detected in the hard X-ray band, represent a new tool to investigate the Universe in a redshift range which is complementary to that covered by other cosmological probes (SNIa and CMB). A review of the Ep-Eiso, Ep-Egamma, Ep-Eiso-tjet, Ep-Liso-T0.45 correlations is presented. Open issues related to these correlations (e.g. presence of outliers and selection effects) and to their use for cosmographic purposes (e.g. dependence on model assumptions) are discussed. Finally, the relevance of thermal components in GRB spectra is discussed in the light of some of the models recently proposed for the interpretation of the spectral-energy correlations.