Characteristics of Diffuse X‐Ray Line Emission within 20 Parsecs of the Galactic Center

Abstract

Over the last three years, the Galactic center region has been monitored with the Chandra X-Ray Observatory. Besides the X-ray emission from the target object, Sgr A*, diffuse X-ray emission was detected throughout most of the 17' × 17' field of view. With 11 Chandra observations through 2002 June, the total effective exposure reaches ~590 ks, providing significant photon statistics on much of the detailed structure within the faint, often filamentary, diffuse X-ray emission. The true-color X-ray image and the equivalent-width images for the detected elemental species of the Galactic center region demonstrate that the diffuse X-ray features have a broad range of spatiospectral properties. Enhancements of the low ionization state Fe line emission (E ~ 6.4 keV) to the northeast of Sgr A* can be interpreted as fluorescence within the dense interstellar medium resulting from irradiation by hard, external X-ray sources. They may also be explained by emission induced by the bombardments by high-energy particles on the ambient medium, such as may accompany unresolved supernova ejecta intruding into dense interstellar medium. The detection of molecular cloud counterparts to the 6.4 keV Fe line-emitting features indicates that these Fe line features are associated with dense Galactic center clouds and/or active star-forming regions, which strongly supports the proposed origins of the X-ray reflection and/or supernova ejecta for the Fe line emission. We detect highly ionized S and Si lines that are generally coincident with the low ionization state Fe line emission and the dense molecular clouds in the northeast of Sgr A*. These hot plasmas are then most likely produced by massive star-forming activities and/or supernova remnants in the Galactic center. In contrast, we find that highly ionized He-like Fe line emission (E ~ 6.7 keV) is primarily distributed along the plane instead of being concentrated in the northeast of Sgr A*. The implied high temperature and the relatively uniform, but strong, alignment along the plane are consistent with the magnetic-confinement model, suggesting that this hot gas component has been reheated by the strong interstellar magnetic fields in the Galactic center to produce the observed He-like Fe line emission.