SRG/eROSITA view of X-ray reflection in the Central Molecular Zone: a snapshot in September-October 2019

TL;DR

This study uses SRG/eROSITA observations from late 2019 to analyze X-ray reflection in the Central Molecular Zone, providing insights into past activity of Sgr A* and properties of molecular clouds through reflection signals.

Contribution

First detailed survey of X-ray reflection in the CMZ from SRG/eROSITA, highlighting the brightest molecular complex Sgr A and discussing scattered radiation features.

Findings

Sgr A complex remains bright in X-ray reflection, suitable for future detailed studies.

Upper limits established for other molecular complexes' X-ray flux.

Identification of scattered radiation features in clouds where primary illumination has passed.

Abstract

X-ray reflection off dense molecular clouds in the Galactic Centre region has established itself as a powerful probe for the past activity record of the supermassive black hole Sgr A* on a timescale of a few hundred years. Detailed studies of the reflection signal from individual clouds allow us to estimate parameters of the brightest flare(s) and explore properties of the dense gas distribution inside and around them. On the other hand, wide area surveys covering the full Central Molecular Zone (CMZ) are crucial to spot brightening of the new clouds and long-term decay of the flux from the once bright ones. Here we present and discuss the data obtained by the SRG/eROSITA telescope in the course of its commissioning observations in late 2019 in regard to the X-ray reflection off CMZ clouds located to the East of Sgr A*. We measure the hard X-ray (4-8 keV) flux from the currently brightest (in reflected emission) molecular complex Sgr A and derive upper limits for other molecular complexes. We confirm that the Sgr A complex keeps being bright at the level of $4\times10^{-13}\, {\rm erg\,s^{-1}\,cm^{-2}\,arcmin^{-2}}$, making it an excellent candidate for the deep forthcoming high resolution imaging and polarimetric observations. We also discuss distinct features of the reflected emission from the clouds for which the primary illumination front has already passed away and the signal is dominated by multiply scattered radiation.