Plasma diagnostics of supernova remnant 3C 400.2 by Suzaku observations

Abstract

We report on the results of plasma diagnostics of the supernova remnant (SNR) 3C 400.2, which has been reported to have a recombining plasma by previous studies. For careful background estimation, we simultaneously fitted spectra extracted from the SNR and background regions and evaluated the SNR emission contaminating the background-region spectrum as well as the background emission in the source-region spectrum. The SNR emission is explained by the collisional ionization equilibrium plasma originating from the interstellar medium and the ionizing plasma originating from the ejecta, in contrast to previous studies. In addition, we found an unidentified X-ray source near the SNR, Suzaku J1937.4$+$1718, which is accompanied by an emission line at $\sim$4.4 keV with a $2.8\sigma$ confidence level. Because there is no striking atomic line at the energy in the rest frame, Suzaku J1937.4$+$1718 could be an extragalactic object with a redshifted Fe line.