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Gamma-ray bursts in 1.8 < z < 5.6 suggest that the time variation of the dark energy is small

Y. Kodama,D. Yonetoku,T. Murakami,S. Tanabe,Ryo Tsutsui,Takashi Nakamura Kyoto University,K. University

Published 2008 in Monthly Notices of the Royal Astronomical Society: Letters

ABSTRACT

We calibrated the peak energy–peak luminosity relation of gamma-ray bursts (GRBs; the so-called Yonetoku relation) using 33 events with redshift z < 1.62 without assuming any cosmological models. The luminosity distances to GRBs are estimated from those of large numbers of Type Ia supernovae with z < 1.755. This calibrated Yonetoku relation can be used as a new cosmic distance ladder towards higher redshifts. We determined the luminosity distances of 30 GRBs in 1.8 < z < 5.6 using the calibrated relation, and plotted the likelihood contour in the (Ωm, ΩΛ) plane. We obtained (Ωm, ΩΛ) = (0.37+0.14−0.11, 0.63+0.11−0.14) for a flat universe. Because our method is free from the circularity problem, we can say that our universe in 1.8 < z < 5.6 is compatible with the so-called concordance cosmological model derived for z < 1.8. This suggests that the time variation of the dark energy is small or zero up to z∼ 6.

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