  The generalized Chaplygin gas, which interpolates between a high density
relativistic era and a non-relativistic matter phase, is a popular dark energy
candidate. We consider a generalization of the Chaplygin gas model, by assuming
the presence of a bulk viscous type dissipative term in the effective
thermodynamic pressure of the gas. The dissipative effects are described by
using the truncated Israel-Stewart model, with the bulk viscosity coefficient
and the relaxation time functions of the energy density only. The corresponding
cosmological dynamics of the bulk viscous Chaplygin gas dominated universe is
considered in detail for a flat homogeneous isotropic
Friedmann-Robertson-Walker geometry. For different values of the model
parameters we consider the evolution of the cosmological parameters (scale
factor, energy density, Hubble function, deceleration parameter and luminosity
distance, respectively), by using both analytical and numerical methods. In the
large time limit the model describes an accelerating universe, with the
effective negative pressure induced by the Chaplygin gas and the bulk viscous
pressure driving the acceleration. The theoretical predictions of the
luminosity distance of our model are compared with the observations of the type
Ia supernovae. The model fits well the recent supernova data. From the fitting
we determine both the equation of state of the Chaplygin gas, and the
parameters characterizing the bulk viscosity. The evolution of the scalar field
associated to the viscous Chaplygin fluid is also considered, and the
corresponding potential is obtained. Hence the viscous Chaplygin gas model
offers an effective dynamical possibility for replacing the cosmological
constant, and to explain the recent acceleration of the universe.
