Archive for arXiv:2205.04623

M87: Ring or Artefact?

Posted in The Universe and Stuff with tags , , on May 13, 2022 by telescoper

Following on from yesterday’s post here is an arXiv preprint that I’ve only just seen, though it was submitted on Tuesday 10th May, ahead of yesterday’s announcement about Sagittarius A*. It says inside the manuscript (though not in the arXiv entry) that it was accepted for publication in ApJ on 5th May, though it has not yet appeared there.

The abstract is:

We report our independent image reconstruction of the M 87 from the public data of the Event Horizon Telescope Collaborators (EHTC). Our result is different from the image published by the EHTC. Our analysis shows that (a) the structure at 230 GHz is consistent with those of lower frequency VLBI observations, (b) the jet structure is evident at 230 GHz extending from the core to a few mas, though the intensity rapidly decreases along the axis, and (c) the unresolved core is resolved into bright three features presumably showing an initial jet with a wide opening angle of about 70 deg. The ring-like structures of the EHTC can be created not only from the public data, but also from the simulated data of a point image. Also, the rings are very sensitive to the FOV size. The u-v coverage of EHT lack about 40 micro-asec fringe spacings. Combining with a very narrow FOV, it created the 40 micro-asec ring structure. We conclude that the absence of the jet and the presence of the ring in the EHTC result are both artifacts owing to the narrow FOV setting and the u-v data sampling bias effect of the EHT array. Because the EHTC’s simulations only take into account the reproduction of the input image models, and not those of the input noise models, their optimal parameters can enhance the effects of sampling bias and produce artifacts such as the 40 micro-asec ring structure, rather than reproducing the correct image.

I draw your attention to the sentence “The ring-like structures of the EHTC can be created not only from the public data, but also from the simulated data of a point image”. In other words the authors (Miyoshi, Kato and Makino) are saying that the ring-like structure in the now-iconic image could be an artefact of the image reconstruction process as they can apparently be produced by a point source.

From the manuscript itself:

The EHTC conducted various surveys, but their methods were not objective and biased towards their desires from the very beginning of their analysis. They also failed to perform the basic data checking that VLBI experts always do.

That’s very blunt. The plot thickens!

It’s a lengthy paper and I haven’t gone through it in detail. Comments from experts are welcome through the box below.