2023/12/05 by Ampuku, Kazuki, Mitsuishi, Ikuyuki, Sakuta, Koki +3
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #Solar and Stellar Astrophysics (astro-ph.SR)
paper · doi:10.48550/arxiv.2312.02551
We analyzed data from HaloSat observations for five fields in the Galactic disk located far away from the Galactic center (135∘ < l < 254∘) to understand the nature of soft X-ray energy emission in the Galactic disk. The fields have 14∘ diameter and were selected to contain no significant high-flux X-ray sources. All five HaloSat soft X-ray energy spectra (0.4--7 keV with energy resolution of <100 eV below 1 keV) show a possibility of the presence of unresolved high-temperature plasma in the Galactic disk (UHTPGD) with a temperature of 0.8--1.0 keV and an emission measure of (8--11)×10-4 \rm cm-6 pc in addition to the soft X-ray diffuse background components mainly studied at higher galactic latitudes (solar wind charge exchange emission, local hot bubble, Milky Way halo emission, and the cosmic X-ray background). This suggests that the UHTPGD is present across the whole Galactic disk. We also observed UHTPGD emission in a region with no bright sources in an \it XMM-Newton field contained within one of the \it HaloSat fields. The temperature and emission measure are consistent with those measured with \it HaloSat. Moreover, the stacked spectra of the X-ray point-like sources and NIR-identified point sources such as stars in the \it XMM-Newton field also show a spectral feature similar to the UHTPGD emission. This suggests that the UHTPGD may partly originate from point-like sources such as stars.