  We analyze the scalar radiation emitted by a source interacting with a
nonminimally coupled scalar field in four-dimensional Schwarzschild--de Sitter
spacetime. We obtain the emission probability using quantum field theory in
curved spacetimes at tree level. We find that the source emits synchrotron-type
radiation for orbits near the photon sphere for all allowed values of the
parameters. We also find that the emitted power strongly depends on the
coupling to the curvature scalar. In particular, the previously observed
enhancement in the contribution of lower multipoles to the emitted power in
this spacetime with minimal coupling is absent when conformal coupling is
considered.
