Imaging an Event Horizon: Mitigation of Scattering Toward Sagittarius A*

TL;DR

This paper demonstrates that scattering effects in millimeter-wavelength VLBI observations of Sagittarius A* can be mitigated by correcting visibilities prior to image reconstruction, enabling clearer imaging of the black hole's relativistic features.

Contribution

The study introduces a method to invert and correct scattering effects in VLBI data, improving the imaging of black hole environments at longer wavelengths.

Findings

Scattering effects can be effectively mitigated through visibility correction.

The technique improves the resolution of GR features in simulated observations.

Method applicable to Sgr A* at wavelengths >= 1.3 mm.

Abstract

The image of the emission surrounding the black hole in the center of the Milky Way is predicted to exhibit the imprint of general relativistic (GR) effects, including the existence of a shadow feature and a photon ring of diameter ~50 microarcseconds. Structure on these scales can be resolved by millimeter-wavelength very long baseline interferometry (VLBI). However, strong-field GR features of interest will be blurred at lambda >= 1.3 mm due to scattering by interstellar electrons. The scattering properties are well understood over most of the relevant range of baseline lengths, suggesting that the scattering may be (mostly) invertible. We simulate observations of a model image of Sgr A* and demonstrate that the effects of scattering can indeed be mitigated by correcting the visibilities before reconstructing the image. This technique is also applicable to Sgr A* at longer wavelengths.