Observation of FE-line emission from sagittarius B2 — Evidence for past activities of our galaxy Original Research Article

We present the ASCA results of imaging spectroscopy of the giant molecular cloud Sgr B2. The X-ray spectrum is found to be very peculiar; it exhibits a strong emission line at 6.4 keV, a low energy cutoff below 4 keV and a pronounced edge-structure at 7.1 keV. The X-ray image is extended and its peak position is shifted in the direction of the Galactic center by about 1–2 arcminute from the core of the molecular cloud. The X-ray spectrum and morphology are well reproduced by a scenario that X-rays from a source located at the Galactic center side are scattered by the molecular cloud Sgr B2, and come into our line of sight. Thus Sgr B2 may be called an X-ray reflection nebula.