The Hubble diagram extended to z >> 1: the gamma-ray properties of gamma-ray bursts confirm the. cold dark matter model

Tight constraints on cosmological parameters can be obtained with standard candles spanning a range of redshifts as large as possible. We propose to treat Type Ia supernovae (SNIa) and long gamma-ray bursts (GRBs) as a single class of candles. Taking advantage of the recent release of the Supernova Legacy Survey and the recent finding of a tight correlation among the energetics and other prompt gamma-ray emission properties of GRBs, we are able to standardize the luminosities/energetics of both classes of objects. In this way we can jointly use GRBs and SNIa as cosmological probes to constrain Omega(m) and Omega(Lambda) and the parameters of the dark energy equation of state through the same Bayesian method that we have, so far, applied to GRBs alone. Despite the large disparity in number (115 SNIa versus 19 GRBs) we show that the constraints on Omega(m) and Omega(Lambda) are greatly improved by the inclusion of GRBs. More importantly, the result of the combined sample is in excellent agreement with the Lambda CDM concordance cosmological model and does not require an evolving equation of state for the dark energy.