Variable Chaplygin Gas: Constraints from Look back Time and SNe Ia(Union 2.1 compilation)

In this paper we try to constrain the parameters of the Variable Chaplygin Gas Model, with equation of state $P=-A(a)/\rho$, where$A(a)$ is a positive function of the scale factor from lookback time measurements of high-z galaxies catalogued in the Gemini Deep Deep Survey(GDDS) and SNe Ia Union2.1\cite{union} Compilation provided by the Supernova Cosmology Project(SCP).