Determine the common origin of non-Gaussian VLBA image noise

Determine whether the non-Gaussian image-noise effects observed in the 7.196 GHz VLBA observations of Orion Nebula Cluster radio sources have the same underlying origin as the analogous effects reported in 1.382 GHz wide-field VLBA observations.

Background

The paper finds excesses in the extreme tails of the VLBA image-pixel distributions relative to a Gaussian model. Because the large search images contain millions of synthesized-beam areas, these non-Gaussian tails materially affect the expected false-positive rate and motivate the adoption of a conservative 7-sigma candidate threshold for the large images.

A similar non-Gaussian noise distribution was reported in earlier wide-field VLBA observations at 1.382 GHz, but the physical origin of the effect was not identified in that work. The present observations show similar behaviour at 7.196 GHz, leaving unresolved whether the two datasets share the same underlying cause.

References

They investigated several different possible causes including different visibility weighting schemes and image averaging which did not resolve the behaviour, and were unable to identify an origin. Their observations were conducted at 1.382 GHz and our observations at 7.196 GHz exhibited similar non-Gaussian behaviour, indicating this could be occurring across different observing frequencies. However, we cannot establish whether the effects have the same underlying origin.

— A VLBA survey of radio stars in the Orion Nebula Cluster: III. Inter-epoch variability analysis  (2609.26466 - O'Kelly et al., 22 Sep 2026) in Section 3, Data Analysis, paragraph following the discussion of image-noise statistics