A Plasmoid Model for the Sgr A* Flares Observed with GRAVITY and Chandra

TL;DR

This paper proposes a plasmoid model for Sgr A* flares that explains observed motions and lightcurve structures using relativistic radiative transfer calculations, offering predictions for future observations.

Contribution

It introduces a novel plasmoid-based model that accounts for the observed flare dynamics and lightcurve features of Sgr A* using general-relativistic simulations.

Findings

The model reproduces the elliptical motion of bright regions observed by GRAVITY.

It explains the occurrence of single and double-peaked flares.

Predictions are made for future observational tests of the model.

Abstract

The Galactic Center black hole Sgr A* shows significant variability and flares in the submillimeter, infrared, and X-ray wavelengths. Owing to its exquisite resolution in the IR bands, the GRAVITY experiment for the first time spatially resolved the locations of three flares and showed that a bright region moves in ellipse-like trajectories close to but offset from the black hole over the course of each event. We present a model for plasmoids that form during reconnection events and orbit in the coronal region around a black hole to explain these observations. We utilize general-relativistic radiative transfer calculations that include effects from finite light travel time, plasmoid motion, particle acceleration, and synchrotron cooling and obtain a rich structure in the flare lightcurves. This model can naturally account for the observed motion of the bright regions observed by the GRAVITY experiment and the offset between the center of the centroid motion and the position of the black hole. It also explains why some flares may be double-peaked while others have only a single peak and uncovers a correlation between the structure in the lightcurve and the location of the flare. Finally, we make predictions for future observations of flares from the inner accretion flow of Sgr A* that will provide a test of this model.