  We investigate the quantum radiation emitted by a uniformly accelerated
Unruh-DeWitt detector in de Sitter spacetime. We find that there exists a
non-vanishing quantum radiation at late times in the radiation zone of the
conformally flat coordinates, which cover the region behind the cosmological
horizon for the accelerated detector. The theoretical structure of producing
the late-time quantum radiation is similar to that of the same model in
Minkowski spacetime: it comes from a nonlocal correlation of the quantum field
in the Bunch-Davies vacuum state, which can be traced back to the entanglement
between the field modes defined in different regions in de Sitter spacetime.
