Constraining Ωm and Dark Energy with Gamma-ray Bursts

An Eγ,jet ∝ E ′ p 1.5 relationship with a small scatter for current γ-ray burst (GRB) data was recently reported, where Eγ,jet is the beaming-corrected γ-ray energy and E ′ p is the νFν peak energy in the local observer frame. By considering this relationship for a sample of 12 GRBs with known redshift, peak energy, and break time of afterglow light curves, we constrain the mass density of the universe and the nature of dark energy. We find that the mass density ΩM = 0.35±0.15 0.15 (at the 1σ confident level) for a flat universe with a cosmological constant, and the w parameter of an assumed static dark-energy equation of state w = −0.84±0.57 0.83 (1σ). Our results are consistent with those from type Ia supernovae. A larger sample established by the upcoming Swift satellite is expected to provide further constraints. Subject headings: cosmological parameters — cosmology: observations — gamma-rays: bursts