Can Gamma-Ray Bursts Be Used to Measure Cosmology? A Further Analysis
نویسندگان
چکیده
Three different methods of measuring cosmology with gamma-ray bursts (GRBs) have been proposed since a relation between the γ-ray energy Eγ of a GRB jet and the peak energy Ep of the νFν spectrum 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 − Ep relation 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 (1σ) for a flat ΛCDM universe. In Method II, to calculate the probability for some certain cosmology, contributions of all the possible Eγ −Ep relations 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 (1σ) for a flat universe. In Method III, to obtain the probability for some cosmology, contributions of all the possible Eγ −Ep relations associated with their unequal weights are considered. With this method, we obtain an inspiring constraint on the mass density 0.16 < ΩM < 0.45 (1σ) for a flat universe, and a χ 2 dof = 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 − Ep relation is calibrated by low-z bursts or not. Ongoing observations on GRBs in the Swift era are expected to make the cosmological utility of GRBs progress from its babyhood into childhood. Subject headings: gamma rays: bursts — cosmology: observations—cosmology: distance scale
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