Gamma-Ray Bursts in $1.8 < z < 5.6$ Suggest that the Time Variation of the Dark Energy is Small

TL;DR

This study calibrates gamma-ray burst relations to measure cosmic distances up to redshift 6, finding that dark energy's properties likely do not vary significantly over this range, supporting the standard cosmological model.

Contribution

It introduces a model-independent calibration of GRB luminosity relations to probe dark energy at high redshifts.

Findings

GRBs can serve as reliable distance indicators up to z~6.

Dark energy shows little to no evolution up to z~6.

Results support the concordance cosmological model at high redshifts.

Abstract

We calibrated the peak energy-peak luminosity relation of GRBs (so called Yonetoku relation) using 33 events with the redshift $z < 1.62$ without assuming any cosmological models. The luminosity distances to GRBs are estimated from those of large amount of Type Ia supernovae with $z<1.755$. This calibrated Yonetoku relation can be used as a new cosmic distance ladder toward 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 $(\Omega_m,\Omega_\Lambda)$ plane. We obtained $(\Omega_m, \Omega_{\Lambda})= (0.37^{+0.14}_{-0.11}, 0.63^{+0.11}_{-0.14})$ for a flat universe. Since 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 $z\sim 6$.