Supernova Ia and Galaxy Cluster Gas Mass Fraction Constraints on Dark   Energy
  We use the Riess et al.(2004) supernova Ia apparent magnitude versus redshift data and the Allen et al.(2004) galaxy cluster gas mass fraction versus redshift data to constrain dark energy models. These data provide complementary constraints that when combined together ignificantly restrict model parameters and favor lowly-evolving dark energy density models, close to the Einstein cosmological constant limit of dark energy. 
Kyle M. Wilson, Gang Chen and Bharat Ratra