Viscous Generalized Chaplygin Gas as a Unified Dark Fluid: Including
  Perturbation of Bulk Viscosity
  In this paper, we continue our previous work of studying viscous generalized
Chaplygin gas (VGCG) as a unified dark fluid but including the bulk viscosity
perturbation. By using the currently available cosmic observational data from
SNLS3, BAO, HST and recently released Planck, we gain the constraint on bulk
viscosity coefficient: $\zeta_0=0.0000138_{- 0.0000105- 0.0000138-
0.0000138}^{+ 0.00000614+ 0.0000145+ 0.0000212}$ in $1, 2, 3\sigma$ regions
respectively via Markov Chain Monte Carlo method. The result shows that when
considering perturbation of bulk viscosity, the currently cosmic observations
favor a smaller bulk viscosity coefficient.
