A Time-Variable X-Ray Echo: Indications of a Past Flare of the Galactic-Center Black Hole

TL;DR

This study analyzes X-ray emissions from the Sgr B2 region, revealing time variability in the 6.40keV iron line that suggests past flaring activity of the Galactic Center black hole Sgr A*.

Contribution

It provides the first evidence of time-variable 6.40keV iron line flux in Sgr B2, supporting the reflection nebula scenario linked to past activity of Sgr A*.

Findings

The 6.40keV line flux varies over time in Sgr B2.

The variability indicates past flaring activity of Sgr A*.

Sgr B2 acts as an X-ray reflection nebula.

Abstract

A time-variability study of the neutral iron line flux at 6.40keV in the Sgr B2 region from data of Suzaku and Chandra is presented. The highly ionized iron line at 6.68keV is due to Galactic Center Diffuse X-rays (GCDX), and is thus time invariable. By comparing the 6.68keV and 6.40keV line fluxes, we found that the 6.40keV flux from the SgrB2 complex region is time variable; particularly the giant molecular cloud M0.66-0.02, known as ``Sgr B2 cloud'' is highly variable. The variability of the 6.40keV line in intensity and spatial distribution strongly supports the scenario that the molecular clouds in the SgrB2 region are X-ray Reflection Nebulae irradiated by the Galactic Center (GC) black hole Sgr A*.