The soft X-ray background with Suzaku: I. Milky Way halo

Masaki Ueda, Hayato Sugiyama, Shogo B. Kobayashi, Kotaro Fukushima, Noriko Y. Yamasaki, Kosuke Sato, Kyoko Matsushita

Submitted on 4 September 2022


We present measurements of the soft X-ray background emission for 130 Suzaku observations at $75^\circ15^\circ$ obtained from 2005 to 2015, covering nearly one solar cycle. In addition to the standard soft X-ray background model consisting of the local hot bubble and the Milky Way Halo (MWH), we include a hot collisional-ionization-equilibrium component with a temperature of $\sim 0.8$ keV to reproduce spectra of a significant fraction of the lines of sight. Then, the scatter in the relation between the emission measure vs. temperature of the MWH component is reduced. Here, we exclude time ranges with high count rates to minimize the effect of the solar wind charge exchange (SWCX). However, the spectra of almost the same lines of sight are inconsistent. The heliospheric SWCX emissions likely contaminate and gives a bias in measurements of temperature and the emission measure of the MWH. Excluding the data around the solar maximum and using the data taken before the end of 2009, at $|b|>35^\circ$ and $105^\circ


Comment: 20 pages, 16 figures, Accepted for publication in PASJ

Subjects: Astrophysics - Astrophysics of Galaxies; Astrophysics - High Energy Astrophysical Phenomena