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

Abstract

We present the results of a closure phase analysis of 3 mm very long baseline interferometry measurements performed on Sagittarius A* (Sgr A*).We have analysed observations made in 2015 May 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.