We present a structural study of the hot ISM in the Galactic halo along the sight line toward the bright active galactic nucleus Mkn 421. The OVII and OVIII absorption lines were measured with the Low Energy Transmission Grating Spectrograph aboard C
handra toward Mkn 421, and the OVII and OVIII emission lines were observed in the adjacent fields of the sight line with the X-ray Imaging Spectrometer aboard Suzaku. We jointly analyzed the absorption and the emission spectra assuming exponential distributions of the gas temperature and density from the Galactic plane, and constrained the temperature and density at the plane to be $(3.2^{+0.6}_{-0.7})times 10^6,mathrm{K}$ and $(1.2^{+0.5}_{-0.4})times 10^{-3},mathrm{cm^{-3}}$, with the scale heights of $1.6^{+1.7}_{-0.7},mathrm{kpc}$ and $>2.8,mathrm{kpc}$ respectively. The results are consistent with those obtained in the LMC X-3 direction and the PKS 2155-304 direction, describing a thick disk-like hot gas with its height of a few kpc from the Galactic plane.
Long-term time variabilities of the OVII (0.57 keV) emission in the soft X-ray diffuse background were studied using six Suzaku annual observations of blank sky towards the Lockman Hole made from 2006 to 2011. After time intervals in which the emissi
on was enhanced on time scales of a few tens of ks were removed, the O VII intensity was found to be constant from 2006 to 2009 within the 90% statistical errors. The intensity in 2010 and 2011 was higher by 2-3 LU (photons/s/cm/sr) than the earlier values. The most plausible origin of the fast variable component is Solar wind charge exchange (SWCX). The intensity increase is not positively correlated with the proton flux at the L1 point. Since all the observations were made in the same season of a year, the variation cannot be explained by parallax of the SWCX induced X-ray emission from the Heliosphere. We consider that it is related to the geometrical change of slow and fast solar wind structures associated with the 11 year solar activity. The observed variation was compared with that expected from the SWCX induced X-ray emission model.
