Constraints On W(0) And W(A) Of Dark Energy From High- Redshift Gamma-Ray Bursts

We extend the Hubble diagram up to z = 5.6 using 63 gamma-ray bursts (GRBs) via peak energy-peak luminosity relation (so-called Yonetoku relation), and obtain constraints on cosmological parameters including dynamical dark energy parametrized by P/rho = w(z) = w(0) + w(a) x z/(1+ z). It is found that the current GRB data are consistent with the concordance model (Omega(m) = 0.28, Omega(Lambda) = 0.72, w(0) =-1, w(a) = 0) within 2 sigma level. Although constraints from GRBs themselves are not so strong, they can improve the conventional constraints from type Ia supernovae because GRBs have much higher redshifts. Further, we estimate the constraints on the dark energy parameters expected by future observations with Gamma-ray Large Area Space Telescope and Swift by Monte Carlo simulation. Constraints would improve substantially with another 150 GRBs.