Plasma diagnostics of supernova remnant 3C 400.2 by Suzaku observations

TL;DR

This study provides a detailed plasma analysis of supernova remnant 3C 400.2 using Suzaku data, revealing equilibrium and ionizing plasma components, and reports a potential extragalactic X-ray source with a redshifted iron line.

Contribution

It offers a refined plasma diagnostic of 3C 400.2 with careful background modeling and identifies a new X-ray source possibly being an extragalactic object.

Findings

SNR plasma is a combination of collisional ionization equilibrium and ionizing plasma.

Background estimation significantly affects plasma diagnostics.

Discovery of an unidentified X-ray source with a redshifted Fe line.

Abstract

We report a result of plasma diagnostics of the supernova remnant (SNR) 3C 400.2, which has been reported to have a recombining plasma (RP) 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 the 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 ~4.4~keV with the 2.8$\sigma$ confidence level. Since there is no striking atomic line at the energy in the rest frame, Suzaku J1937.4+1718 can be an extragalactic object with a redshifted Fe line.