Suzaku Observation of the Southeastern Rim of the Cygnus Loop

Abstract

Abstract X-ray measured metal abundances of the rim of the Cygnus Loop are known to have two patterns. One, seen at narrow regions along the outermost edge, is 0.5-times the solar value, and the other, seen in the remainder of the rim, is 0.2-times the solar value. While the former is “normal”, as the ISM around the Cygnus Loop, the latter is unexpectedly depleted, and its origin has been puzzling. We have been tackling this issue by observing the rims with X-ray observatories. So far, the normal abundance was observed only at regions where no cloud-shock interactions are suggested. On the contrary, based on our recent Suzaku observations, we find the normal abundance at the southeastern rim where cloud-shock interactions are evident. The spatial variation of the abundance there is similar to that in other normal abundance rims: the normal abundance is present along the outermost edge (4$^\prime$ width regions), while the inner region shows strongly depleted abundances. This structure has been confirmed both by the plasma model fit and by the model-free fit. We noticed that the rim regions showing normal abundance correspond to those with a relatively weak radio intensity. Since the Cygnus Loop is believed to be the result of a cavity explosion, we discuss that the abundance distribution is due to the abundance difference between the cavity wall and its outside. The origin of the depleted abundance still remains an open question.