Confirmation of stimulated Hawking radiation, but not of black hole lasing

Stimulated Hawking radiation in an analogue black hole in a Bose-Einstein condensate was reported seven years ago, and it was claimed that the stimulation was of the black hole lasing variety. The study was based on observation of rapidly-growing negative-energy waves. We find that the Hawking particles are directly observable in the experimental plots, which confirms the stimulated Hawking radiation. We further verify this result with new measurements. Also, the observed Hawking particles provide a sensitive, background-free probe of the underlying mechanism of the stimulation. The experiment inspired the prediction of the Bogoliubov-Cherenkov-Landau (BCL) mechanism of stimulated Hawking radiation. By computing the Bogoliubov coefficient for Hawking radiation, we find that the stimulation was of the BCL type, rather than black-hole lasing. We further confirm the results with numerical simulations of both black hole lasing and BCL stimulation.