I had a skim through the article in astronomy and astrophysics and I saw this
> The ring’s appearance in the images reconstructed with different algorithms (MiRA and IRBis) lends support to it being real. However, as Fig. E.2 shows, the location of the ring is just inside the side lobe of the dirty beam, and therefore we cannot entirely exclude the possibility that it might be an artifact of the image reconstruction inherent in the imperfect uv coverage. We refrain from further discussing this structure until we can confirm it with better uv coverage.
Which is interesting. So the ring may be an artifact.