X-Ray Spectrum of a Peculiar Supernova Remnant G359.1-0.5

TL;DR

This paper reports Suzaku X-ray observations of supernova remnant G359.1-0.5, revealing over-ionized plasma with unique spectral features, indicating extreme ionization conditions not explained by standard models.

Contribution

It provides the first detailed analysis of over-ionized plasma in G359.1-0.5, demonstrating the presence of radiative recombination continua and fitting the spectrum with an over-ionized plasma model.

Findings

Detection of strong RRC structures indicating over-ionization

Best-fit electron temperature of 0.29 keV and ionization temperature of 0.77 keV

G359.1-0.5 is in an extreme over-ionized state

Abstract

We present the Suzaku results of a supernova remnant (SNR), G359.1-0.5 in the direction of the Galactic center region. From the SNR, we find prominent K-shell lines of highly ionized Si and S ions, together with unusual structures at 2.5-3.0 and 3.1-3.6 keV. No canonical SNR plasma model, in either ionization equilibrium or under-ionization, can explain the structures. The energies and shapes of the structures are similar to those of the radiative transitions of free electrons to the K-shell of He-like Si and S ions (radiative recombination continuum: RRC). The presence of the strong RRC structures indicates that the plasma is in over-ionization. In fact, the observed spectrum is well fitted with an over-ionized plasma model. The best-fit electron temperature of 0.29 keV is far smaller than the ionization temperature of 0.77 keV, which means that G359.1-0.5 is in extreme condition of over-ionization. We report some cautions on the physical parameters, and comment possible origins for the over-ionized plasma.