Methods for detecting flaring structures in Sagittarius A* with high frequency VLBI

TL;DR

This paper explores high-frequency VLBI techniques to detect and analyze flaring structures in Sagittarius A*, focusing on hot-spot models and developing non-imaging algorithms to identify periodic signals.

Contribution

It introduces new interferometric closure-based algorithms for detecting periodic structures in Sagittarius A* using millimeter VLBI, applicable to various models.

Findings

Structural periodicity can be detected with modern VLBI arrays.

Enhanced VLBI arrays improve periodicity detection capabilities.

Methods are adaptable to different models of Sagittarius A*.

Abstract

The super massive black hole candidate, Sagittarius A*, exhibits variability from radio to X-ray wavelengths on time scales that correspond to < 10 Schwarzschild radii. We survey the potential of millimeter-wavelength VLBI to detect and constrain time variable structures that could give rise to such variations, focusing on a model in which an orbiting hot spot is embedded in an accretion disk. Non-imaging algorithms are developed that use interferometric closure quantities to test for periodicity, and applied to an ensemble of hot-spot models that sample a range of parameter space. We find that structural periodicity in a wide range of cases can be detected on most potential VLBI arrays using modern VLBI instrumentation. Future enhancements of mm/sub-mm VLBI arrays including phased array processors to aggregate VLBI station collecting area, increased bandwidth recording, and addition of new VLBI sites all significantly aid periodicity detection. The methods described herein can be applied to other models of Sagittarius A*, including jet outflows and Magneto-Hydrodynamic accretion simulations.