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Do temporarily accelerated particles experience the Unruh effect? I think, they don't, because they don't see an apparent event horizon.

On the other hand, if the duration of the acceleration is long enough, this case should be approximated during this phase by the eternal accelerated particle. And this particle sees the Unruh effect.

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up vote 3 down vote accepted

There is also an Unruh effect for not eternally accelerated observers! See Akhmedov, Singleton, "On the physical meaning of the Unruh effect", . There is even a derivation of Unruh effect for observers moving on a circle (which don't see an event horizon too) with a fascinating connection to the Sokolov-Ternov effect of high energy physics.

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Will the distribution of modes as observed by a finitely accelerated observer be thermal? – Prathyush Apr 3 '13 at 22:56
No, the spectrum observed by an detector on a circular path is not thermal. This comes from the form of the 2-point-function for circular motion, see eq. 5 in above mentioned paper. It is quite different from the 2-point-function of eternal linear acceleration, which is strongly connected to a Planckian thermal distribution. – AGP Apr 4 '13 at 8:48

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