Lookback time and Chandra constrains on cosmological parameters
  In this paper we combine the WMAP7 with lookback time and Chandra gas fraction data to constrain the main cosmological parameters and the equation of state for the dark energy. We find that the lookback time is a good measurement that can improve the determination of the equation of state for the dark energy with regard to other external data sets. We conclude that larger lookback time data set will further improve our determination of the cosmological parameters. 
D. Tonoiu, A.Caramete, L.A. Popa
astro-ph.CO