New Constraints on Cosmic Particle Populations at the Galactic Center using X-ray Observations of the Molecular Cloud Sagittarius B2

TL;DR

This study uses recent X-ray observations of Sagittarius B2 to investigate cosmic ray populations and their interactions, providing new constraints on low-energy cosmic rays in the Galactic Center.

Contribution

It offers the first detailed analysis of small-scale X-ray variations in Sgr B2 and sets upper limits on low-energy cosmic ray interactions using recent deep observations.

Findings

Detected small-scale X-ray variations in Sgr B2

Provided upper limits on low-energy cosmic ray interactions

Compared Fe Kα fluxes across different cloud densities

Abstract

The Sagittarius B2 (Sgr B2) molecular cloud complex is an X-ray reflection nebula whose total emissions have continued to decrease since 2001 as it reprocesses one or more past energetic outbursts from the supermassive black hole Sagittarius A*. The X-ray reflection model explains the observed time variability and provides a window into the luminous evolutionary history of our nearest supermassive black hole. In light of evidence of elevated cosmic particle populations in the Galactic Center, X-rays from Sgr B2 are also of interest as a probe of low-energy (sub-GeV) cosmic rays, which may be responsible for an increasing relative fraction of the nonthermal X-ray emission as the contribution from X-ray reflection decreases. Here, we present the most recent deep NuSTAR and XMM-Newton observations of Sgr B2, from 2018. These reveal small-scale variations within lower-density portions of the complex, including brightening features, yet still enable upper limits on X-rays from low-energy cosmic particle interactions in Sgr B2. We present Fe K$\alpha$ fluxes from cloud regions of different densities, facilitating comparison with models of ambient LECR interactions throughout the cloud.