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 K alpha lines from highly ionized ions of various elements has confir med the presence of an extended high-temperature plasma. The fluoresce nt X-ray emission from cold iron atoms in molecular clouds was also fo und, 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-average d energy generation rate comparable to Seyfert nuclei, a class of acti ve galactic nuclei.