The soft diffuse X-ray emission of twelve fields observed with Suzaku are presented together with two additional fields from previous analyses. All have galactic longitudes 65$^\circ $$\lt$$\ell$$\lt$ 295$^\circ $ to avoid contributions from the very bright diffuse source that extends at least 30$^\circ $ from the Galactic center. The surface brightnesses of the Suzaku nine fields for which apparently uncontaminated ROSAT All Sky Survey (RASS) were available were statistically consistent with the RASS values, with an upper limit for differences of 17 $\times$ 10$^{-6}$cs$^{-1}$arcmin$^{-2}$ in R45-band. The OVII and OVIII intensities are well correlated to each other, and OVII emission shows an intensity floor at $\sim$2 photonss$^{-1}$cm$^{-2}$str$^{-1}$ (LU). The high-latitude OVIII emission shows a tight correlation with excess of OVII emission above the floor, with (OVIII intensity) $=$ 0.5 $\times$ [(OVII intensity) $-$ 2LU], suggesting that temperatures averaged over different line-of-sight show a narrow distribution around $\sim$0.2 keV. We consider that the offset intensity of OVII arises from the Heliospheric solar wind charge exchange and perhaps from the local hot bubble, and that the excess OVII (2–7LU) is emission from more distant parts of the Galaxy. The total bolometric luminosity of this galactic emission is estimated to be 4 $\times$ 10$^{39}$ergs$^{-1}$, and its characteristic temperature may be related to the virial temperature of the Galaxy.

Although about 40% of the soft X-ray background emission in 0.4 to 1 keV range has extragalactic origins and thus is totally blocked by the galactic absorption in midplane directions, it decreases at most by about 20% in midplane. Suzaku observation of the direction, ($\ell$, $b$) $=$ (235$^\circ$, 0$^\circ$), showed an O vii${\rm K} \alpha$ emission intensity comparable with that of the MBM-12 on cloud Suzaku observation, but revealed a narrow bump peaked at $\sim$0.9 keV. The latter component is partly filling the decrease of the extragalactic component in midplane. The feature can be well represented by a thin thermal emission with a temperature of about 0.8 keV. Because of the high pressure implied for spatially extended hot gas, the emission is likely a sum of unresolved faint sources. We consider a large fraction of the emission originates from faint dM stars. We constructed a model spectrum for spatially unresolved dM stars that consistently explains the observed spectrum and the surface brightness. The model also suggests that the emission from dM stars decreases very rapidly with increasing $b$, and thus that it cannot compensate entirely the decrease of the extragalactic component at $b$$\sim$ 2$^\circ$–10$^\circ$.

We observed an X-ray afterglow of GRB 060904A with the Swift and Suzaku 1 satellites. We found rapid spectral softening during both the prompt tail phase and the decline phase of an X-ray flare in the BAT and XRT data. The observed spectra were fit by power-law photon indices which rapidly changed from Γ = 1.51 +0.04 −0.03 to Γ = 5.30 +0.69 −0.59 within a few hundred seconds in the prompt tail. This is one of the steepest X-ray spectra ever observed, making it quite difficult to explain by simple electron acceleration and synchrotron radiation. Then, we applied an alternative spectral fitting using a broken power-law with exponential cutoff (BPEC) model. It is valid to consider the situation that the cutoff energy is equivalent to the synchrotron frequency of the maximum energy electrons in their energy distribution. Since the spectral cutoff appears in the soft X-ray band, we conclude the electron acceleration has been inefficient in the internal shocks of GRB 060904A. These cutoff spectra suddenly disappeared at the transition time from the prompt tail phase to the shallow decay one. After that, typical afterglow spectra with the photon indices of 2.0 are continuously and preciously monitored by both XRT and Suzaku/XIS up to 1 day since the burst trigger time. We could successfully trace the temporal history of two characteristic break energies (peak energy and cutoff energy) and they show the time dependence of ∝ t −3 ∼ t −4 while the following afterglow spectra are quite stable. This fact indicates that the emitting material of prompt tail is due to completely different dynamics from the shallow decay component. Therefore we conclude the emission sites of two distinct phenomena obviously differ from each other.

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