Suzaku observation of the Galactic Ridge K.Ebisawa,T.Takahashi, H.Murakami, Y.Ezoe (ISAS), Y.Tanaka (MPE), S.Yamauchi (Iwate), K.Koyama (Kyoto), M.Kokubun, H.Takahashi (Tokyo), A.Bamba, A.Senda (RIKEN), Y.Fukazawa, T.Mizuno (Hiroshima), H.Tsunemi (Osaka), T.Kohmura (Kogakuin), J.Hughes (Rutgers) and the Suzaku team Origin of the Galactic Ridge X-ray Emission (GRXE) has been a big mystery for more than 20 years. Ebisawa et al. (2001,2005) carried out a deep Chandra observation on a Galactic plane blank field at (l,b)~(28. 5,0. 0), and indicated that only ~10 % of the 2-10 keV GRXE emission is resolved into point sources down to ~3× ergs s -1 cm -2. This strongly suggests diffuse origin of GRXE. However, Revnivtsev et al. (2005) recently pointed out an extremely strong spatial correlation between the 3  m IR (which is supposed to represent stellar emission) and GRXE maps. This might indicate that a significant part of GRXE is due to stellar point sources. Spectroscopic observation with Suzaku, whose effective area exceeds that of Chandra and background is lower than XMM-Newton, is expect to give a crucial key of GRXE through plasma diagnostic. Suzaku observation was made on the same Chandra field on Oct. 28, 2005 for 100 ksec. Left is the Chandra image and right is Suzaku image. We found a Chandra point source, CXOGPE J is brightned during the Suzaku observation. Light curve and energy spectrum of CXOGPE J are shown below. The flare- like variation, relatively hard spectrum, and hint of narrow iron line at ~6.7 keV suggests this source is a Galactic cataclysmic variable. CXO GPEJ Chandra Suzaku Three FI chips combined Bgd Cal source Iron lines BI FI Main purpose of the observation is spectral study of the diffuse emission, in particular precise study of the iron K-band. We made energy spectrum excluding the point source CXOGPE J As indicated in the left figure BI has a strong background in the iron K-band, so we concentrate on the FI chips for the time being. We have not subtracted background yet. Three FI chips are averaged, and we fitted the spectrum in 4-10 keV with a phenomenological broken-power-law + gaussian model. In addition to three iron lines, we needed four gaussians to describe the calibration source (5.87 keV) and background lines (7.47 keV, 8.25 keV and 9.69 keV). We used the responses ae_xi0_ rmf and ae_xi0_onaxis_ arf. Three iron line parameters are determined as follows (note, absolute flux is not precise, since ARF is not correctly normalized). *E=6.43 keV, f=5.73e-6 photons/s/cm 2 /XIS *E=6.66 keV, f=9.98e-6 photons/s/cm 2 /XIS *E=6.99 keV, f=2.06e-6 photons/s/cm 2 /XIS We did not detect finite breadths of the lines. All the line widths (iron lines, calibration source line, BGD lines) are consistent with being infinitesimal. Although present results are very preliminary, we already got hints of important discoveries: (1) We clearly detect three iron K-lines, from low ionized species, He-like ions and H-like ions. It has been pointed out that centroid of the iron K-line (if fitted with a single line) is ~6.5 keV, significantly lower than what is expected from He-like ions (Kaneda et al. 1997; Ebisawa et al. 2005). We found that this is due to the presence of 6.4 keV line in addition to the 6.67 keV line. (2) Iron lines are not obviously broadened. This does not support the Charge-exchange model by Tanaka (2002), where significant line broadening is expected from bulk motion of cosmic-ray iron ions. We were not able to constrain the iron line intrinsic width being limited by photon statistics. Another 100 ksec observation on the save field scheduled in March will enable us to make more conclusive results.