  It is investigated the gravitational waves phenomena in the geometric scalar
theory of gravity (GSG), a class of theories such that gravity is described by
a single scalar field. The associated physical metric describing the spacetime
is constructed from a disformal transformation of Minkowski geometry. In this
theory, a weak field approximation gives rise to a description similar to that
one obtained in general relativity, with the gravitational waves propagating at
the same speed as the light, although they have a characteristic longitudinal
polarization mode, besides others modes that are observer dependent. We also
analyze the energy carried by the gravitational waves as well as how their
emission affects the orbital period of a binary system. Observational data
coming from Hulse and Taylor binary pulsar is then used to constraint the
theory parameter.
