Probing the thermal character of analogue Hawking radiation for shallow water waves?

Understand

We study and numerically compute the scattering coefficients of shallow water waves blocked by a stationary counterflow.

• When the flow is transcritical, the coefficients closely follow Hawking's prediction according to which black holes should emit a thermal spectrum.
• We study how the spectrum deviates from thermality when reducing the maximal flow velocity, with a particular attention to subcritical flows since these have been recently used to test Hawking's prediction.
• For such flows, we show that the emission spectrum is strongly suppressed, and that its Planckian character is completely lost.