The GammaRay Burst Hubble Diagram and Its Implications for Cosmology
Abstract
In this paper, we continue to build support for the proposal to use gammaray bursts (GRBs) as standard candles in constructing the Hubble diagram at redshifts beyond the current reach of Type Ia supernova observations. We confirm that correlations among certain spectral and lightcurve features can indeed be used as luminosity indicators, and demonstrate from the most uptodate GRB sample appropriate for this work that the ΛCDM model optimized with these data is characterized by parameter values consistent with those in the concordance model. Specifically, we find that (\Omega _m,\Omega _\Lambda)\approx (0.25_{0.06}^{+0.05}, 0.75_{0.05}^{+0.06}), which are consistent, to within 1σ, with (0.29, 0.71) obtained from the 9 yr Wilkinson Microwave Anisotropy Probe data. We also carry out a comparative analysis between ΛCDM and the R _{h} = ct universe and find that the optimal ΛCDM model fits the GRB Hubble diagram with a reduced \chi ^2_dof\approx 2.26, whereas the fit using R _{h} = ct results in a \chi ^2_dof\approx 2.14. In both cases, about 20% of the events lie at least 2σ away from the bestfit curves, suggesting that either some contamination by nonstandard GRB luminosities is unavoidable or that the errors and intrinsic scatter associated with the data are being underestimated. With these optimized fits, we use three statistical tools—the Akaike information criterion, the Kullback information criterion, and the Bayes information criterion—to show that, based on the GRB Hubble diagram, the likelihood of R _{h} = ct being closer to the correct model is ~85%96%, compared to ~4%15% for ΛCDM.
 Publication:

The Astrophysical Journal
 Pub Date:
 July 2013
 DOI:
 10.1088/0004637X/772/1/43
 arXiv:
 arXiv:1301.0894
 Bibcode:
 2013ApJ...772...43W
 Keywords:

 cosmology: observations;
 cosmology: theory;
 dark energy;
 early universe;
 gammaray burst: general;
 Astrophysics  High Energy Astrophysical Phenomena;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 39 pages, 7 figures, 2 tables, accepted for publication in ApJ