Tracing Dark Energy History with Gamma-Ray Bursts

Observations of gamma-ray bursts up to z similar to 9 are best suited to study the possible evolution of the universe equation of state at intermediate redshifts. We apply the Combo relation to a sample of 174 gamma-ray bursts to investigate possible evidence of evolving dark energy parameter w(z). We first build a gamma-ray burst Hubble's diagram and then we estimate the set (omega(m), omega(?)) in the framework of flat and non-flat ?CDM paradigm. We then get bounds over the wCDM model, where w is thought to evolve with redshift, adopting two priors over the Hubble constant in tension at 4.4 sigma, i.e., H-0 = (67.4 0.5) km s(-1) Mpc(-1) and H-0 = (74.03 1.42) km s(-1) Mpc(-1). We show our new sample provides tighter constraints on omega(m) since at z <= 1.2 we see that w(z) agrees within 1 sigma with the standard value w = -1. The situation is the opposite at larger z, where gamma-ray bursts better fix w(z) that seems to deviate from w = -1 at 2 sigma and 4 sigma level, depending on the redshift bins. In particular, we investigate the w(z) evolution through a piecewise formulation over seven redshift intervals. From our fitting procedure we show that at z >= 1.2 the case w < -1 cannot be fully excluded, indicating that dark energy's influence is not negligible at larger z. We confirm the Combo relation as a powerful tool to investigate cosmological evolution of dark energy. Future space missions will significantly enrich the gamma-ray burst database even at smaller redshifts, improving de facto the results discussed in this paper.

Automated summary

Observations of gamma-ray bursts up to z similar to 9 are best suited for studying the possible evolution of the universe equation of state at intermediate redshifts. By applying the Combo relation to a sample of 174 gamma-ray bursts, possible evidence of evolving dark energy parameter w(z) is investigated. The study reveals that dark energy's influence may not be negligible at larger redshifts, with potential deviations from the standard value of w = -1.