Improved cosmological constraints on the curvature and equation of state of dark energy

We apply the Constitution compilation of 397 supernova Ia, the baryon acoustic oscillation measurements including the A parameter, the distance ratio and the radial data, the five-year Wilkinson microwave anisotropy probe and the Hubble parameter data to study the geometry of the Universe and the property of dark energy by using the popular Chevallier-Polarski-Linder and Jassal-Bagla-Padmanabhan parameterizations. We compare the simple chi(2) method of joined contour estimation and theMonte Carlo Markov chain method, and find that it is necessary to make the marginalized analysis on the error estimation. The probabilities of Omega(k) and w(a) in the Chevallier-Polarski-Linder model are skew distributions, and the marginalized 1 sigma errors are Omega(km) = 0.279(-0.008)(+0.015), Omega(k) = 0.005(-0.011)(+0.006), w(0) = -1.05(-0.06)(+0.23) and w(a) = 0.5(-1.5)(+0.3). For the Jassal-Bagla-Padmanabhan model, the marginalized 1s errors are Omega(m) = 0.281(-0.01)(+0.015), Omega(k) = 0.000(-0.006)(+0.007), w(0) = -0.96(-0.18)(+0.25) and w(a) = -0.6(-1.6)(+1.9). The equation of state parameter w(z) of dark energy is negative in the redshift range 0 <= z <= 2 at more than 3 sigma level. The flat Lambda CDM model is consistent with the current observational data at the 1s level.