Can gamma-ray bursts be used to measure cosmology? a further analysis.
XU D., DAI Z.G. and LIANG E.W.
Abstract (from CDS):
Three different methods of measuring cosmology with gamma-ray bursts (GRBs) have been proposed since a relation between the gamma-ray energy Eγof a GRB jet and the peak energy Epof the νFνspectrum in the burst frame was reported by Ghirlanda and coauthors. In method I, to calculate the probability for a favored cosmology, only the contribution of the Eγ-Eprelation that is already best-fitted for this cosmology is considered. We apply this method to a sample of 17 GRBs and obtain the mass density ΩM=0.15+0.45–0.13(1 σ) for a flat ΛCDM universe. In method II, to calculate the probability for some certain cosmology, contributions of all the possible Eγ-Eprelations that are best-fitted for their corresponding cosmologies are taken into account. With this method, we find a constraint on the mass density 0.14<ΩM<0.69 (1 σ) for a flat universe. In method III, to obtain the probability for some cosmology, contributions of all the possible Eγ-Eprelations associated with their unequal weights are considered. With this method, we obtain an inspiring constraint on the mass density 0.16<ΩM<0.45 (1 σ) for a flat universe and χ2dof=19.08/15=1.27 for the concordance model of ΩM=0.27. Compared with the previous two methods, method III makes the observed 17 GRBs place much more stringent confidence intervals at the same confidence levels. Furthermore, we perform a Monte Carlo simulation and use a larger sample to investigate the cosmographic capabilities of GRBs with different methods. We find that a larger GRB sample could be used to effectively measure cosmology, no matter whether the Eγ-Eprelation is calibrated by low-z bursts or not. Ongoing observations of GRBs in the Swift era are expected to make the cosmological utility of GRBs progress from its babyhood into childhood.