7 data. This is also visible in Figure \[fig:almab6b7\] and is an important feature that could shed light on the origin of this gap. We also compute a spectral index map using multi-frequency clean (<span style="font-variant:small-caps;">nterms</span>=2) and natural weights. The bottom panel of Figure \[fig:radial\_profile\] shows the azimuthally averaged radial profile of the spectral index (${\alpha_\mathrm{mm}}$). From 40 to 150 au the disc has spectral index of roughly $2.7\pm0.1$ (assuming ${\alpha_\mathrm{mm}}$ is constant over radii), consistent with the overall spectral index estimated above. Note that uncertainties on ${\alpha_\mathrm{mm}}$ do not include the 10% absolute flux uncertainties as we are only interested in relative differences as a function of radius.

In addition to the outer disc, we detect emission from within 30 au that peaks near the stellar position in the azimuthally averaged profile. However, it has a much higher level than the photospheric emission if we extrapolate this from available photometry at wavelengths shorter than 10$\mu$m using a Rayleigh-Jeans spectral index ($F_{\nu \star}=32\pm1$ and $18\pm1$ $\mu$Jy at 0.86 and 1.1 mm, respectively). Moreover, between 20 and 30 au we also find that ${\alpha_\mathrm{mm}}$ has a peak of $\sim3.7$, although still within $2\sigma$ from the average spectral index. In §\[sec:parmodel\] we 