  The recent observational evidences for the present accelerated stage of the
Universe have stimulated renewed interest for alternative cosmologies. In
general, such models contain an unknown negative-pressure dark component that
explains the supernova results and reconciles the inflationary flatness
prediction ($\Omega_{\rm{T}} = 1$) and the cosmic microwave background
measurements with the dynamical estimates of the quantity of matter in the
Universe ($\Omega_{\rm{m}} \simeq 0.3 \pm 0.1$). In this paper we study some
observational consequences of a dark energy candidate, the so-called
generalized Chaplygin gas which is characterized by an equation of state $p_{C}
= -A/\rho_{C}^{\alpha}$, where $A$ and $\alpha$ are positive constants. We
investigate the prospects for constraining the equation of state of this dark
energy component by combining Chandra observations of the X-ray luminosity of
galaxy clusters, independent measurements of the baryonic matter density, the
latest measurements of the Hubble parameter as given by the HST Key Project and
data of the Supernova Cosmology Project. We show that very stringent
constraints on the model parameters can be obtained from this combination of
observational data.
