Origin of the low-temperature plasma in the Galactic center X-ray emission

Abstract

Abstract The Galactic Center X-ray emission (GCXE) is composed of high-temperature (∼7 keV) and low-temperature (∼1 keV) plasmas (HTP and LTP, respectively). The global structure of the HTP is roughly uniform over the Galactic Center (GC) region, and the origin of the HTP has been extensively studied. On the other hand, the LTP is more clumpy, and its origin has not been studied in detail. In the S xv Heα line map, a pair of horn-like soft diffuse sources are seen at symmetric positions with respect to Sagittarius A⋆. The X-ray spectra of the pair are well represented by an absorbed thin thermal plasma model of temperature and NH of 0.6–0.7 keV and 4 × 1022 cm−2, respectively. The NH values indicate that the pair are located near the GC. Then the dynamical time scales of the pair are ∼105 yr. The Si and S abundances and the surface brightnesses in the S xv Heα line band are 0.7–1.2 and 0.6–1.3 solar, and (2.0–2.4) × 10−15 erg s−1 cm−2 arcmin−2, respectively. The temperature, abundances, and surface brightness are similar to those of the LTP in the GCXE, while the abundances are far larger than those of known point sources, typically coronal active stars and RS CVn-type active binaries. Based on these results, the possible origin of the LTP is discussed.