The X-ray footprint of the CircumNuclear Disk

TL;DR

This study used extensive Chandra X-ray observations to reveal that the CircumNuclear Disk acts as a barrier rather than an absorber, shaping the diffuse X-ray emission in the Galactic Centre.

Contribution

First detection of a depression in X-ray luminosity corresponding to the CND, with detailed spectral analysis showing its role as a plasma barrier and its composition dominated by shock-heated ejecta.

Findings

CND acts as a barrier for Galactic Centre plasma

X-ray diffuse emission is a two-temperature plasma with super-solar abundances

CND's iron abundance indicates shock-heated ejecta from a supernova remnant

Abstract

We studied the central regions of the Galactic Centre to determine if the CircumNuclear Disk (CND) acts as an absorber or a barrier for the central X-rays diffuse emission. After reprocessing 4.6Ms of Chandra observations, we were able to detect, for the first time, a depression in the X-ray luminosity of the diffuse emission whose size and location correspond to those of the CND. We extracted the X-ray spectra for various regions inside the CND footprint as well as for the region where the footprint is observed and for a region located outside the footprint. We simultaneously fitted these spectra as an optically thin plasma whose absorption by the interstellar medium and by the local plasma were fitted independently using the MCMC method. The hydrogen column density of the ISM is 7.5x10^22 cm^-2. The X-ray diffuse emission inside the CND footprint is formed by a 2T plasma of 1 and 4keV with slightly super-solar abundances except for the iron and carbon which are sub-solar. The plasma from the CND, in turn, is better described by a 1T model with abundances and local hydrogen column density which are very different to those of the innermost regions. The large iron abundance in this region confirms that the CND is dominated by the shock-heated ejecta of the Sgr A East supernova remnant. We deduced that the CND rather acts as a barrier for the Galactic Centre plasma and that the plasma located outside the CND may correspond to the collimated outflow possibly created by Sgr A* or the interaction between the wind of massive stars and the mini-spiral material.