Super-Poynting vector and comoving observers in the Einstein-Rosen spacetime

In this work we used the concept of super-energy flux in General Relativity and the monad formalism of Ehlers-Zelmanov to find the comoving observers with the Einstein-Rosen cylindrical gravitational waves and obtained their corresponding 3-velocity of propagation with respect to a family of observers locally at rest. Therefore, we found that the aforementioned waves propagate at subluminal speed in vacuum.