ASCA View of Our Galactic Center: Remains of Past Activities in X-Rays?

Detailed X-ray images and spectra of the galactic-center region up to 10 keV were obtained with ASCA. Diffuse thermal-emission with distinct Kalpha lines from highly ionized ions of various elements has confirmed the presence of an extended high-temperature plasma. The fluorescent X-ray emission from cold iron atoms in molecular clouds was also found, possibly due to irradiation by X-rays from the center, which was bright in the past, but is presently dim. The results suggest that the galactic center exhibited intermittent activities with a time-averaged energy generation rate comparable to Seyfert nuclei, a class of active galactic nuclei.