Suzaku View of the Galactic Center Diffuse X-ray Emission

There is unresolved X-ray emission prevailing over the Galactic center region, which is called as the Galactic center diffuse X-ray emission (GCDX). 10--30% of the GCDX is resolved into point sources by Chandra observations (e.g., Revnivtsev et al. 2006, A\&A, 453, 253). Extended sources, such as supernova remnants and/or X-ray reflection nebulae, may contribute to some part of the GCDX. Nature and origin of the remaining component are still under investigation. The most characteristic feature of the GCDX is prominent Fe-K lines at 6.4 (Fe I), 6.7 (Fe XXV) and 7.0 keV (Fe XXVI). We have surveyed toward the GC region and on the Galactic plane with Suzaku. The longitudinal distribution of the 6.7 keV line is different from that of infrared stars, and shows X-ray excesses on the GC. The scale height along the Galactic latitude of the 6.4 keV line is $\sim$0.22 and $\sim$0.5 degree for the GC and plane, respectively. Those of the 6.7 keV line are $\sim$0.26 and $\sim$1.0 degree, respectively. These facts, therefore, indicate that main origins of the Fe lines are different. We focused on the Fe-line band spectrum in 5--10 keV, and compared that of the GCDX and those of candidate classes, active binaries and cataclysmic variables, for the point source scenario. We found that any combination of the point sources cannot explain the GCDX spectrum, especially the 6.4 and 6.7 keV lines. The GCDX should contain unknown origins other than ABs and CVs, and would be possibly related with high energy phenomena in GC.