Curvature properties and Ricci solitons of Lorentzian pr-waves manifolds

We study the curvature properties of Lorentzian pr-waves manifolds. Several interesting examples are found, in particular as regards local symmetry, conformal flatness and Einstein-like metrics. The existence of non-trivial (i.e., not Einstein) Ricci solitons on conformally flat pr-waves manifolds is proved. Moreover, we show that only steady Ricci solitons may be gradient.