Optically thin hot plasma near the Galactic center - Mapping observations of the 6.7 keV iron line

Results of 6.7 keV emission-line mapping observations of the Galactic center region are reported. The 6.7 keV emission line is attributable to a helium-like iron K-shell transition in an optically thin hot plasma of a temperature about 10 to the 8th K. The surface brightness distribution of the plasma is elliptical with a major axis of 1.8 deg (FWHM) and an axial ratio of about 0.5. The major axis is tilted about 20 deg with respect to the Galactic plane. The total flux and surface brightness of the extended X-ray emission in the continuum X-ray band are determined to be (1-3) x 10 to the -9th ergs/s sq cm and (2-5) x 10 to the -6th ergs/s sq cm in 2-10 keV, respectively. The equivalent width of the iron line is estimated to be 500-1300 eV, consistent with the value expected for a cosmic iron abundance. Several possibilities of the origin of the extended plasma are considered. 22 refs