in the BH frame, the BCR can stimulate production of Hawking pairs at the BH horizon. (Zero frequency Hawking pairs do not exist.)

The stimulated HR is seen in the spacetime portrait Fig. \[fig:stimulated\_HR\](b). The BCR first reaches the BH at $t\approx 20$ ms, stimulating emission of HR. Hawking radiation first appears at around 25 ms, but is not visible on the grayscale plot until around 40 ms. The left–moving partner radiation (p-mode) resulting from the “pair creation" forms a “V"-shape with the HR, and makes an interference pattern with the BCR that can first be seen around $t\approx 40$ ms. (Were there no mode present to stimulate the pair creation, it would nevertheless occur spontaneously, as in the Hawking effect for an astrophysical black hole.)

Figure \[fig:stimulated\_HR\](a) is a schematic illustration of the mechanism just described. This is viewed in the laboratory frame, where the BH moves at velocity $v_s$ and the WH with a slightly smaller velocity, $v_s-\Delta v$, as indicated by the dashed red line. As seen by inspection of Fig. \[fig:stimulated\_HR\](b), the BCR (i.e., the standing wave) has zero phase velocity with respect to the WH, corresponding to zero frequency in the WH frame. Since the 