The Jet and Resolved Features of the Central Supermassive Black Hole of M87 Observed with the Event Horizon Telescope (EHT)

We report the result of our independent image reconstruction of the M87 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 very long baseline interferometry observations, (b) the jet structure is evident at 230 GHz extending from the core to a few milliarcsecond, although the intensity rapidly decreases along the axis, and (c) the unresolved core is resolved into three bright features presumably showing an initial jet with a wide opening angle of similar to 70 degrees. 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 field-of-view (FOV) size. The u-v coverage of the Event Horizon Telescope (EHT) lacks similar to 40 mu as fringe spacings. Combining with a very narrow FOV, it created the similar to 40 mu as 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 similar to 40 mu as ring structure, rather than reproducing the correct image.

Automated summary

We present an independent image reconstruction of M87 using public data from the Event Horizon Telescope Collaborators (EHTC). Our results differ from the image published by EHTC. Our analysis shows that the structure at 230 GHz is consistent with lower-frequency observations, the jet structure is evident at 230 GHz extending from the core, and the unresolved core reveals three bright features indicative of an initial jet. Furthermore, we suggest that the presence of ring-like structures in the EHTC result is an artifact caused by the narrow field-of-view setting and the u-v data sampling bias effect.