Abundance Inhomogeneity in the Northern Rim of the Cygnus Loop

We observed the northern rim of the Cygnus Loop with the Suzaku observatory in 5 pointings (P21-P25). From a spatially resolved analysis, all of the spectra were well fitted by a single component of the non-equilibrium ionization plasma model. From the best-fit parameters, we found that the abundances of the heavy elements are significantly lower than the solar values, except for those at the outermost edge in P21 and P22. The origin of the depleted metal abundances is still unclear, while such deficiencies have been reported from many other rim observations of the Loop. To explain these depletions at the rim regions, we considered several possibilities. The effects of resonance-line-scattering and grain condensation lower the values of the abundances. However, these are not sufficient to account for the observed abundance depletion. We found that the abundances at the outermost edge in P21 and P22 are higher than those at the other regions. From a morphological point of view, it is reasonable to consider that this abundance inhomogeneity is derived from the breakout or the thinness of the cavity wall of the Loop.