The luminosity distance vs . redshift law is now measured using supernovae and \gamma -ray bursts , and the angular size distance is measured at the surface of last scattering by the CMB and at z = 0.35 by baryon acoustic oscillations .
In this paper this data is fit to models for the equation of state with w = -1 , w = constant , and w ( z ) = w _ { 0 } + w _ { a } ( 1 - a ) .
The last model is poorly constrained by the distance data , leading to unphysical solutions where the dark energy dominates at early times unless the large scale structure and acoustic scale constraints are modified to allow for early time dark energy effects .
A flat \Lambda CDM model is consistent with all the data .