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Date and Time of the Query: 2019-06-26 T03:05:49 PDT
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For refcode 2015A&A...582A.115I:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
2015A&A...582A.115I New measurements of Omega_m_ from gamma-ray bursts Izzo, L.; Muccino, M.; Zaninoni, E.; Amati, L.; Della Valle, M. 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 E_p,i_, the X-ray afterglow initial luminosity L_0_ and the rest-frame duration tau of the shallow phase, and the index of the late power-law decay {alpha}_X_. We use it to measure Omega_m_ 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 E_p,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 Omega_M_ = 0.29^+0.23^_-0.15_ (1sigma) for the LambdaCDM cosmological model, and Omega_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 Omega_m_ with an accuracy comparable to that exhibited by SNe Ia, and to investigate the dark energy contribution and evolution up to z ~ 10. Key words: cosmological parameters, gamma-ray burst: general, dark energy
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