The updated E_peak - E_gamma correlation in GRBs
  The recently discovered correlation between the rest frame GRB peak spectral energy $E_{\rm peak}$ and the collimation corrected energy $E_\gamma$ in long GRBs is potentially very important, yet awaits confirmation from an independent sample. It may help to shed light on the radiation mechanism of the prompt GRB phase and on the way -- and in which form -- the energy is released from the central engine. We here present some additional evidence for the correlation (two new bursts) and re-derive the best-fit parameters. The tightness of the correlation is confirmed (sigma=0.1 dex). We show that this correlation allows us, for the first time, to use GRBs as cosmological probes to constrain the expansion history of the universe. 
G. Ghirlanda (1), G. Ghisellini (1), D. Lazzati (2), C. Firmani (1)   ((1) Oss. Astr. di Brera; (2) JILA, U. of Colorado)