Figure 1

The scattering potential $V_a$ [defined in Eq. (5)] is plotted for different values of the angular momentum $l$. We can see that it vanishes at the canonical acoustic hole horizon ($r=r_H$). As $r\to \infty$, $V_a$ falls as $1/r^6$ for $l=0$ and as $1/r^2$ for $l>0$.Reuse & Permissions

Figure 2

The partial absorption cross section ${\sigma }_a^{(l)}$ is plotted as a function of the wave frequency $\omega$, for $l=0$ up to $l=6$. Note that the larger $l$ is, the smaller is the corresponding maximum of ${\sigma }_a^{(l)}$.Reuse & Permissions

Figure 3

The total absorption cross section ${\sigma }_a$ is plotted as a function of the wave frequency $\omega$. The summation in Eq. (14) is performed up to $l=6$. It starts equal to the black hole horizon area and falls approaching ${\sigma }_a^{hf}$ (see dashed line), in complete agreement with the results obtained in the low- and high-frequency approximations.Reuse & Permissions