GRB cosmology through the Ep,I-intensity correlation

Abstract

Despite they are not standard candles, the investigation of Gamma-Ray Bursts (GRBs) as a tool for measuring the geometry and expansion rate of the Universe is strongly motivated by their unique combination of huge luminosity, up to more than 10^53 erg/s, with a redshift distribution extending up to more than z = 9. In recent years, several attempts to exploit the correlation between the photon energy at which the vFv spec- trum peaks (peak energy) and the radiated energy (or luminosity) for standardizing GRBs and using them to estimate cosmological parameters have been made. These studies show that already with the present data-set, GRBs can provide a significant and independent confirmation of Omega_M ∼ 0.3 for a flat ΛCDM. The investigation of the correlation of Ep,i with different intensity indicators (e.g., radiated energy, average and peak luminosity, bolometric vs. monochromatic quantities, etc.) both in terms of intrinsic dispersion of and accuracy for estimating Imega_M further confirms its reliability and effectiveness for both GRB physics and their standardization for cosmology. Current (e.g., Swift, Fermi/GBM, Konus-WIND) and forthcoming GRB experiments (e.g., CALET/GBM, SVOM, Lomonosov/UFFO) will allow us to constrain Omega_M with an accuracy comparable to that currently exhibited by Type Ia supernovae and to study the properties of dark energy and their evolution with time.