We studied the energy spectrum and the large-scale fluctuation of the X-ray background with the ASCA GIS instrument based on the ASCA Medium Sensitivity Survey and Large Sky Survey observations. A total of 91 fields with Galactic latitude |b| > 10 • were selected with a sky coverage of 50 deg 2 and 4.2 Ms of exposure. For each field, non X-ray events were carefully subtracted and sources brighter than ∼ 2 × 10 −13 erg cm −2 s −1 (2-10 keV) were eliminated. Spectral fits with a single power-law model for the individual 0.7-10 keV spectra showed a significant excess below ∼ 2 keV, which could be expressed by an additional thermal model with kT ≃ 0.4 keV or a steep power-law model with a photon index of Γ soft ≃ 6. The 0.5-2 keV intensities of the soft thermal component varied significantly from field to field by 1 σ = 52 +4 −5 %, and showed a maximum toward the Galactic Center. This component is considered to be entirely Galactic. As for the hard power-law component, an average photon index of 91 fields was obtained to be Γ hard = 1.412 ± 0.007 ± 0.025 and the average 2-10 keV intensity was calculated as F hard X = (6.38 ± 0.04 ± 0.64) × 10 −8 erg cm −2 s −1 sr −1 (1 σ statistical and systematic errors). The Galactic component is marginally detected in the hard band. The 2-10 keV intensities show a 1 σ deviation of 6.49 +0.56 −0.61 %, while deviation due to the reproducibility of the particle background is 3.2%. The observed deviation can be explained by the Poisson noise of the source count in the f.o.v. (∼ 0.5 deg 2 ), even assuming a single logN -logS relation on the whole sky. Based on the observed fluctuation and the absolute intensity, an acceptable region of the log N -log S relation was derived, showing a consistent feature with the recent Chandra and XMM-Newton results. The fluctuation of the spectral index was also examined; it implied a large amount of hard sources and a substantial variation in the intrinsic source spectra (Γ S ≃ 1.1 ± 1.0).

Recent developments of transition-edge sensors (TESs), based on extensive experience in ground-based experiments, have been making the sensor techniques mature enough for their application on future satellite cosmic microwave background (CMB) polarization experiments. LiteBIRD is in the most advanced phase among such future satellites, targeting its launch in Japanese Fiscal Year 2027 (2027FY) with JAXA's H3 rocket. It will accommodate more than 4000 TESs in focal planes of reflective low-frequency and refractive medium-and-high-frequency telescopes in order to detect a signature imprinted on the CMB by the primordial gravitational waves predicted in cosmic inflation. The total wide frequency coverage between 34 and 448 GHz enables us to extract such weak spiral polarization patterns through the precise subtraction of our Galaxy's foreground emission by using spectral differences among CMB and foreground signals. Telescopes are cooled down to 5 K for suppressing thermal noise and contain polarization modulators with transmissive half-wave plates at individual apertures for separating sky polarization signals from artificial polarization and for mitigating from instrumental 1/f noise. Passive cooling by using V-grooves supports active cooling with mechanical coolers as well as adiabatic demagnetization refrigerators. Sky observations from the second Sun-Earth Lagrangian point, L2, are planned for 3 years.

satellite: JAXA's new strategic L-class mission for all-sky surveys of cosmic microwave background polarization,"