  One of the key ingredients for making binary waveform predictions in a
beyond-GR theory of gravity is understanding the energy and angular momentum
carried by gravitational waves and any other radiated fields. Identifying the
appropriate energy functional is unclear in Hassan-Rosen bigravity, a
ghost-free theory with one massive and one massless graviton. The difficulty
arises from the new degrees of freedom and length scales which are not present
in GR, rendering an Isaacson-style averaging calculation ambiguous. In this
article we compute the energy carried by gravitational waves in bigravity
starting from the action, using the canonical current formalism. The canonical
current agrees with other common energy calculations in GR, and is unambiguous
(modulo boundary terms), making it a convenient choice for quantifying the
energy of gravitational waves in bigravity or any diffeomorphism-invariant
theories of gravity. This calculation opens the door for future waveform
modeling in bigravity to correctly include backreaction due to emission of
gravitational waves.
