Abstract

We present the fit of a constant bulk viscosity model to observational data, where the dark sector of the cosmic substratum is a viscous fluid with pressure p = −ζ, being ζ the fluid-expansion scalar and ζ the coefficient of bulk viscosity. We use the updated sample of 59 high-redshift GRBs, reported by Wei (2010) and calibrated at low redshifts with the Union 2 sample of SNe Ia. Testing the constant bulk viscosity model with GRBs we found the best fit for the viscosity parameter ζ̃ is in the range 0<ζ̃<3, being consistent with previous probes.

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