Characteristics of Diffuse X-ray Line Emission within 20 Pc of the Galactic Center

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 spatio-spectral 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 which 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 this hot gas component has been re-heated by the strong interstellar magnetic fields in the Galactic center to produce the observed He-like Fe line emission. Subject headings: Galaxy: center – ISM: clouds – X-rays: individual (Sagittarius A East, Sagittarius A*) – X-rays: ISM