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Abstract

We develop an adiabatic formalism to study the Hawking phenomenon from the perspective of Unruh-DeWitt detectors moving along non-stationary, non-asymptotic trajectories. When applied to geodesic trajectories, this formalism yields surprising results: (i) though they have zero acceleration, the temperature measured by detectors on circular orbits is higher than that measured by static detectors at the same distance from the hole, and diverges on the photon sphere, (ii) in the near-horizon region, both outgoing and incoming modes excite infalling detectors, and, for highly bound trajectories ($E\ll1$), the latter actually dominate the former, (iii) in this region, the relationship between the temperature of Hawking radiation and the relative velocity between the detector and the hole is not of Doppler type. We confirm the apparent perception of high-temperature ingoing Hawking radiation by infalling observers with $E\ll1$ by a flux computation. We close by a discussion of the role played by spacetime curvature on the near-horizon Hawking radiation.