Recently, X-ray observations revealed that some of evolved supernova remnants (SNRs) have plasmas in which the recombination process becomes more dominant than the ionization process. In most of these SNRs having the recombining plasma (RP), association of molecular and atomic clouds are observed. This implies that the evolution of SNRs are considered to be deeply related to the environment of the ambient gas, though they are not fully understood. In order to study physical and astrophysical causes of the formation of the RP in evolved SNRs, we develop a new framework that provides both X-ray spectra and images of evolved SNRs with an age of > 104 yr. Our model calculates the time evolution of temperatures of electron and ions, which are not considered in previous plasma models, based on a one-dimensional Lagrangian hydrodynamics simulation. We include physical processes of shock heating, energy exchange by Coulomb interaction, radiative cooling and evolution of ionization states. The spectra are composed of bremsstrahlung and emissions by atomic transition of major elements calculated from atomic properties of AtomDB. Since effects of the surrounding environment of SNRs is important in their evolution, we investigate the relation between plasma states in SNRs and interstellar medium (ISM) density using our model by changing ISM density (1, 3, 10, and 30 cm-3). In our simulation, the RP is naturally produced in evolved SNRs (~ 104 yr) which exploded in the dense ISM. We characterize spectra by the electron temperature and ionization temperature that is an indicator of describing the ionization state. As a result of comparing these temperatures of our model with the observations, we successfully demonstrate that the time evolution of ionization and recombination are in excellent agreement with the observed values. Our model holds promising application for future X-ray missions with a high resolution spectrometer.
Scientific local contacts: O. Limousin, D Renaud, organizer: M. Galametz
