Measuring cosmology with Gamma-Ray Bursts

Gamma-Ray Bursts (GRBs) are becoming more and more standardizable candles. Different methods have been proposed to measure cosmology with the relation between the γ-ray energy Eγ of a GRB jet and the peak energy Ep of the νFν spectrum in the burst frame. We compare the procedures and results of these methods. Using the present sample of 17 GRBs, we obtain a constraint on the mass density ΩM 0.22-0.07+0.42 (1σ) for a flat ACDM universe with the median circumburst density n ≅ 3.0 cm-3. Theoretical investigations of the Eγ α Epa relation reach a ∼ 1.5. A larger sample in the Swift era is expected to provide further constraints on the GRB cosmography