Uniform distribution of the extremely overionized plasma in the SNR G359.1-0.5 and its implication for the SNR evolution

X-ray plasmas called recombining plasmas (RPs; plasmas with higher ionization temperatures than electron temperatures) in supernova remnants (SNRs) have been found in 16 objects. These RPs are considered as important components to understand SNR evolution, since their origins have been thought to be closely related to their local environment. The supernova remnant (SNR) G359.1-0.5 is located along the line of sight towards the Galactic center, and is known to have a peculiar RP. The X-ray emission shows the most prominent radiative recombination continuum emission of silicon among known recombining SNRs. We report on the results of our detailed analyses on the RP of G359.1-0.5, and the interacting CO clouds. Combining Chandra and Suzaku data, we estimated the ionization state of the plasma with a careful treatment of the background spectrum. The average spectrum shows a remarkably large deviation of the electron temperature ($\sim$0.17 keV) from the initial temperature ($>$16 keV), indicating that the plasma is in a highly recombination-dominant state. We also searched for spatial variation of the plasma parameters, but found no significant differences. Using $^{12}$CO (J=2-1) data obtained with NANTEN2, we also found a plausible candidate for the interacting CO cloud, which is surrounding the SNR. The estimated distance to the cloud is $\sim$4 kpc, which indicates that this SNR is not located in the Galactic center region. These results indicate that the SNR has experienced extremely rapid cooling and subsequent expansion into the cavity region, and has begun to interact with the ambient cloud.