Unruh radiation normally applies to linearly accelerated frames
Is there an equivalent of the Unruh thermal radiation in a frame that is spinning? I am not aware of any horizon being created from a spinning frame, so I presume that no thermal photons should be expected?
Apparently there is, but it is somewhat complicated since there is ambiguity of what constitutes a circularly accelerated coordinate system.
This paper, On the physical meaning of the Unruh effect by Akhmedov and Singleton derives a formula for the Unruh effect in circular motion. They find that the spectrum experienced is not Planckian and do not get a closed form equation for it, but the same effect is there. This paper gives the temperature as $$T\approx \frac{\hbar a}{2\sqrt{3}ck_B}.$$ In the linear acceleration formula $2\sqrt{3}$ is replaced by $2\pi$.
(There is also this paper showing a nonlinear dependency; I have a feeling this result depends on using a different set of coordinates.)
