  We study the theory of relativistic viscous hydrodynamics introduced in
arXiv:1109.0985 and arXiv:1907.12695, which provided a causal and stable
first-order theory of relativistic fluids with viscosity in the case of
barotropic fluids. The local well-posedness of its equations of motion has been
previously established in Gevrey spaces. Here, we improve this result by
proving local well-posedness in Sobolev spaces.
