We derive new constraints set by SNIa experiments ( ‘ gold ’ data sample of Riess et al . ) , X-ray galaxy cluster data ( Allen et al . Chandra measurements of the X-ray gas mass fraction in 26 clusters ) , large scale structure ( Sloan Digital Sky Survey spectrum ) and cosmic microwave background ( WMAP ) on the quartessence Chaplygin model .
We consider both adiabatic perturbations and intrinsic non-adiabatic perturbations such that the effective sound speed vanishes ( Silent Chaplygin ) .
We show that for the adiabatic case , only models with equation of state parameter | \alpha| \lesssim 10 ^ { -2 } are allowed : this means that the allowed models are very close to \Lambda CDM .
In the Silent case , however , the results are consistent with observations in a much broader range , -0.3 < \alpha < 0.7 .