Molecular clouds: X-ray mirrors of the Galactic nuclear activity

TL;DR

This study analyzes X-ray emissions from Galactic Centre Molecular Clouds over 8 years, suggesting they reflect past activity of Sgr A* with evidence of a significant flare about a century ago.

Contribution

It provides evidence that X-ray reflections in molecular clouds are caused by a historic flare of Sgr A*, revealing insights into the Galactic nucleus activity history.

Findings

Super-luminal motion of X-ray light front observed

X-ray emission decrease in G0.11-0.11 similar to Sgr B2

Luminosity consistent with a flare of Sgr A* 100 years ago

Abstract

We present the result of a study of the X-ray emission from the Galactic Centre Molecular Clouds (MC), within 15 arcmin from Sgr A*. We use XMM-Newton data spanning about 8 years. We observe an apparent super-luminal motion of a light front illuminating a MC. This might be due to a source outside the MC (such as Sgr A* or a bright and long outburst of a X-ray binary), while it can not be due to low energy cosmic rays or a source located inside the cloud. We also observe a decrease of the X-ray emission from G0.11-0.11, behaviour similar to the one of Sgr B2. The line intensities, clouds dimensions, columns densities and positions with respect to Sgr A*, are consistent with being produced by the same Sgr A* flare. The required high luminosity (about 1.5 10^39 erg s-1) can hardly be produced by a binary system, while it is in agreement with a flare of Sgr A* fading about 100 years ago.