Asymmetric structure in Sgr A* at 3mm from closure phase measurements with VLBA, GBT and LMT

TL;DR

This paper analyzes 3mm VLBI closure phase data of Sgr A* from VLBA, GBT, and LMT, revealing asymmetric structure likely due to intrinsic source features or scattering effects.

Contribution

It introduces a simple two-component model fitting VLBI data to reveal asymmetry in Sgr A* at 3mm, advancing understanding of its structure.

Findings

Detected non-zero closure phases indicating asymmetry.

Favored a model with a fainter component east of the main source.

Discussed possible causes including intrinsic asymmetry or scattering substructure.

Abstract

We present the results of a closure phase analysis of 3 mm very long baseline interferometry (VLBI) measurements performed on Sagittarius A* (Sgr A*). We have analyzed observations made in May 2015 using the Very Long Baseline Array, the Robert C. Byrd Green Bank Telescope and the Large Millimeter Telescope Alfonso Serrano and obtained non-zero closure phase measurements on several station triangles - indicative of a non-point-symmetric source structure. The data are fitted with an asymmetric source structure model in Sgr A*, represented by a simple two-component model, which favours a fainter component due East of the main source. This result is discussed in light of a scattering screen with substructure or an intrinsically asymmetric source.