New measurements of Ωm from gamma-ray bursts
Journal
Date Issued
2015
Author(s)
Description
We thank the referee for her/his constructive comments which have improved the paper. E.Z. acknowledges the support by the International Cooperation Program CAPES-ICRANet financed by CAPES – Brazilian Federal Agency for Support and Evaluation of Graduate Education within the Ministry of Education of Brazil. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester.
Abstract
Context. Data from cosmic microwave background radiation (CMB), baryon acoustic oscillations (BAO), and supernovae Ia (SNe-Ia) support a constant dark energy equation of state with w_0 ~ -1. Measuring the evolution of w along the redshift is one of the most demanding challenges for observational cosmology. Aims: We discuss the existence of a close relation for gamma-ray bursts (GRBs), named Combo-relation, based on characteristic parameters of GRB phenomenology such as the prompt intrinsic peak energy Ep,i, the X-ray afterglow initial luminosity L0 and the rest-frame duration τ of the shallow phase, and the index of the late power-law decay α_X. We use it to measure Ωm and the evolution of the dark energy equation of state. We also propose a new calibration method for the same relation, which reduces the dependence on SNe Ia systematics.
Methods: We have selected a sample of GRBs with 1) a measured redshift z; 2) a determined intrinsic prompt peak energy Ep,i; and 3) a good coverage of the observed (0.3-10) keV afterglow light curves. The fitting technique of the rest-frame (0.3-10) keV luminosity light curves represents the core of the Combo-relation. We separate the early steep decay, considered a part of the prompt emission, from the X-ray afterglow additional component. Data with the largest positive residual, identified as flares, are automatically eliminated until the p-value of the fit becomes greater than 0.3. Results: We strongly minimize the dependency of the Combo-GRB calibration on SNe Ia. We also measure a small extra-Poissonian scatter of the Combo-relation, which allows us to infer from GRBs alone Ω_M = 0.29(+0.23,-0.15) (1σ) for the ΛCDM cosmological model, and Ω_M = 0.40(+0.22, -0.16), w_0 = -1.43(+0.78,-0.66) for the flat-Universe variable equation of state case. Conclusions: In view of the increasing size of the GRB database, thanks to future missions, the Combo-relation is a promising tool for measuring Ω_m with an accuracy comparable to that exhibited by SNe Ia, and to investigate the dark energy contribution and evolution up to z ~ 10.
Methods: We have selected a sample of GRBs with 1) a measured redshift z; 2) a determined intrinsic prompt peak energy Ep,i; and 3) a good coverage of the observed (0.3-10) keV afterglow light curves. The fitting technique of the rest-frame (0.3-10) keV luminosity light curves represents the core of the Combo-relation. We separate the early steep decay, considered a part of the prompt emission, from the X-ray afterglow additional component. Data with the largest positive residual, identified as flares, are automatically eliminated until the p-value of the fit becomes greater than 0.3. Results: We strongly minimize the dependency of the Combo-GRB calibration on SNe Ia. We also measure a small extra-Poissonian scatter of the Combo-relation, which allows us to infer from GRBs alone Ω_M = 0.29(+0.23,-0.15) (1σ) for the ΛCDM cosmological model, and Ω_M = 0.40(+0.22, -0.16), w_0 = -1.43(+0.78,-0.66) for the flat-Universe variable equation of state case. Conclusions: In view of the increasing size of the GRB database, thanks to future missions, the Combo-relation is a promising tool for measuring Ω_m with an accuracy comparable to that exhibited by SNe Ia, and to investigate the dark energy contribution and evolution up to z ~ 10.
Volume
582
Start page
A115
Issn Identifier
0004-6361
Ads BibCode
2015A&A...582A.115I
Rights
open.access
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