Chandra Observation of the Cluster of Galaxies MS 0839.9+2938 at   z=0.194: the Central Excess Iron and SN Ia Enrichment
  We present the Chandra study of the intermediately distant cluster of galaxies MS 0839.9+2938. By performing both the projected and deprojected spectral analyses, we find that the gas temperature is approximately constant at about 4 keV in 130-444h_70^-1 kpc. In the inner regions, the gas temperature descends towards the center, reaching <~ 3 keV in the central 37h_70^-1 kpc. This infers that the lower and upper limits of the mass deposit rate are 9-34 M_sun yr^-1 and 96-126 M_sun yr^-1, respectively within 74h_70^-1 kpc where the gas is significantly colder. Along with the temperature drop, we detect a significant inward iron abundance increase from about 0.4 solar in the outer regions to about 1 solar within the central 37h_70^-1 kpc. Thus MS 0839.9+2938 is the cluster showing the most significant central iron excess at z>~ 0.2. We argue that most of the excess iron should have been contributed by SNe Ia. By utilizing the observed SN Ia rate and stellar mass loss rate, we estimate that the time needed to enrich the central region with excess iron is 6.4-7.9 Gyr, which is similar to those found for the nearby clusters. Coinciding with the optical extension of the cD galaxy (up to about 30h_70^-1 kpc), the observed X-ray surface brightness profile exhibits an excess beyond the distribution expected by either the beta model or the NFW model, and can be well fitted with an empirical two-beta model that leads to a relatively flatter mass profile in the innermost region. 
Yu Wang (SJTU, NAOC, BNU), Haiguang Xu (SJTU), Zhongli Zhang (SJTU),   Yueheng Xu (SJTU), Xiang-Ping Wu (NAOC), Sui-Jian Xue...