GRB cosmology through the Ep - intensity correlation: status and perspectives

Author: Lorenzo Amati

Abstract: Given their huge isotropic-equivalent radiated energies, up to more than 1054 erg, and their redshift distribution extending up to more than z = 8, Gamma-Ray Bursts (GRB) are in principle a powerful tool for measuring the geometry and expansion rate of the Universe. However, they are not standard candles given that their luminosities span several orders of magnitude, even when considering possible collimation angles. In the recent years, several attempts to exploit the correlation between the photon energy at which the nuFnu spectrum peaks (``peak energy'') and the radiated energy (or luminosity) for ``standardizing'' GRBs and using them as tools, complementary to other probes like SN Ia, BAO and the CMB, for the estimate of cosmological parameters have been made. These studies show that already with the present data set GRBs can provide a significant and independent confirmation of ΩM < 1 (and around 0.25) for a flat LambdaCDM universe and that the measurements expected from present and next GRB experiments (e.g. Swift, Fermi/GBM, SVOM, UFFO) will allow us to constrain ΩM, ΩΛ, and, in particular, to get clues on dark energy properties and evolution