The Physical Origin and Time Lag of Multi-Frequency Flares from SgrA*

TL;DR

This study uses advanced GRMHD simulations and radiative transfer calculations to identify the origin of multi-frequency flares from SgrA*, linking polarity inversion events to observed time delays across wavelengths.

Contribution

It demonstrates that large-scale polarity inversion in a multi-loop magnetic field configuration can explain the origin and timing of flares from SgrA* using comprehensive simulations.

Findings

Polarity inversion events generate 138 THz flares consistent with observations.

Time delays between frequencies are caused by plasma self-absorption effects.

Flaring regions shift outward over time, affecting observed frequencies.

Abstract

Sagittarius~A$^*$, the supermassive black hole at the center of our galaxy, exhibits flares across various wavelengths, yet their origins remain elusive. We performed 3D two-temperature General Relativistic Magnetohydrodynamic (GRMHD) simulations of magnetized accretion flows initialized from multi-loop magnetic field configuration onto a rotating black hole and conducted General Relativistic Radiative Transfer (GRRT) calculations considering contributions from both thermal and non-thermal synchrotron emission processes. Our results indicate that the polarity inversion events from the multi-loop magnetic field configurations can generate $138\,\rm THz$ flares consistent with observations with the help of non-thermal emission. By tracing the intensity evolution of light rays in GRRT calculations, we identify the precise location of the flaring region and confirm that it originates from a large-scale polarity inversion event. We observe time delays between different frequencies, with lower-frequency radio flares lagging behind higher frequencies due to plasma self-absorption in the disk. The time delay between near-infrared and 43 GHz flares can reach up to $\sim 50$ min, during which the flaring region gradually shifts outward, becoming visible at lower frequencies. Our study confirms that large-scale polarity inversion in a Standard And Normal Evolution (SANE) accretion flow with a multi-loop initial magnetic configuration can be a potential mechanism driving flares from Sgr~A$^*$.