Constraining the Flaring Region of Sagittarius A* By 1.3mm VLBI Measurements

TL;DR

This paper models the flaring region of Sagittarius A* using 1.3mm VLBI data, constraining flare locations and orientations, and compares hot-spot and jet scenarios to interpret the observed variability near the black hole.

Contribution

It introduces a method to interpret VLBI measurements of Sgr A*'s flares, constraining their positions and orientations, and compares different physical models for the flare origin.

Findings

Flare distance from black hole constrained to less than 20 Rg east-west.

Flare likely passes in front of black hole at larger radius in hot-spot model.

Jet ejection angle estimated to be greater than 40 degrees from the black hole axis.

Abstract

We use a model of an accretion flow coupled with an emergent flare to interpret the latest 1.3mm VLBI measurements for Sagittarius A*. The visibility data constrained the distances from the flare center to the black hole center as $d_{\rm EW}\lesssim20{\rm R_g}$ and $d_{\rm NS}\lesssim80{\rm R_g}$ in the East-West and North-South directions, respectively. If interpreted by the hot-spot model, the flare was preferred to pass in front of the black hole at a radius much larger than $d_{\rm EW}$. If interpreted by the episodic jet launched from a nearly edge-on hot accretion flow, the flare was preferred to be ejected with $\theta_{\rm j}\gtrsim40^\circ$ off the black hole rotating axis. This method can be generalized to help us understand future sub-millimeter VLBI observations, and study the millimeter/sub-millimeter variabilities in the vicinity of the Galactic Center supermassive black hole.