X-ray emission from the mixed-morphology supernova remnant HB 9

We present the results of a spectral analysis of the central region of the mixed-morphology supernova remnant HB 9. A prior Ginga observation of this source detected a hard X-ray component above 4 keV, and the origin of this particular X-ray component is still unknown. Our results demonstrate that the extracted X-ray spectra are best represented by a model consisting of a collisional ionization equilibrium plasma with a temperature of ∼0.1-0.2 keV (interstellar matter component) and an ionizing plasma with a temperature of ∼0.6-0.7 keV and an ionization timescale of >1 × 10¹¹ cm^-3 s (ejecta component). No significant X-ray emission was found in the central region above 4 keV. The recombining plasma model reported by a previous work does not explain our spectra.