Deep X-Ray Observations of Supernova Remnants G359.1–0.5 and G359.0–0.9 with ASCA

We present the results of deep ASCA observations of two shell-like radio supernova remnants (SNRs) located in the direction to the galactic center (GC) region. Unlike the radio morphology, G359.1-0.5 shows center-filled X-rays with prominent Kα lines of He-like silicon and H-like sulfur. The plasma requires at least two temperature components: a silicon-dominated cool plasma of 0.6 keV temperature and a sulfur-dominated higher temperature plasma of 4.4 keV. Because the absorption column is ∼ 6× 1022 H cm-2, this SNR would be near to the GC. The spherical plasma is attributable to supernova ejecta with the total mass of Si and S being about 0.1 M⊙ and 0.3 M⊙, respectively. X-rays from G359.0-0.9 trace the partial shell structure of the radio emission. The spectrum is well fitted to a single-temperature plasma of 0.4 keV with a non-solar abundance of magnesium or iron. Because the absorption column is not very large, ∼ 1.8× 1022 H cm-2, G359.0-0.9 would be in front of the GC region. The total supernova energy, interstellar density near to the X-ray emitting shell, and age of the SNR are estimated to be 1.2× 1051 erg, 0.5 cm-3, and 1.8× 104 yr, respectively. We also discuss possible implications on the origin of the large-scale hot plasma surrounding the GC.