Study of the X-Ray Background Spectrum and its Large-Scale Fluctuation with ASCA

By A. Kushino, Y. Ishisaki, U. Morita, N. Yamasaki, M. Ishida, T. Ohashi, Y. Ueda. 2002

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We studied the energy spectrum and the large-scale fluctuation of the X-ray background with the ASCA GIS based on the ASCA MSS and LSS observations. A total of 91 fields with Galactic latitude |b|>10 deg were selected with a sky coverage of 50 deg^2 and 4.2 Ms of exposure. For each field, sources brighter than \sim 2\times 10^{-13}\ergs (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 \sim 2 keV, which could be expressed by an additional thermal model with kT\simeq 0.4 keV or a steep power-law model with photon index GS\simeq 6. The 0.5-2 keV intensities of the soft thermal component varied significantly by 1\sigma=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 GH = 1.412\pm 0.007\pm 0.025 and the average 2-10 keV intensity was calculated as FH = (6.38\pm 0.04\pm 0.64)\times 10^{-8} \ergss. The Galactic component is marginally detected in the hard band. The 2-10 keV intensities shows a 1\sigma deviation of 6.49^{+0.56}_{-0.61}%, while deviation due to the NXB is 3.2%. The observed deviation can be explained by the Poisson noise of source count in the f.o.v. (\sim 0.5 deg^2), even assuming a single \logn relation on the whole sky. Based on the observed fluctuation and the absolute intensity, an acceptable region of the \logn relation was derived, showing a consistent feature with the recent Chandra and XMM-Newton results. Fluctuation of the spectral index was also examined, and it implied a large amount of hard sources and a substantial variation in the intrinsic source spectra (GS\simeq 1.1\pm 1.0).

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/53c7a719478981cf96d0124523b8fa0fc6452bd5

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In Astronomy and Astrophysics

1. W. N. Brandt
2. D. M. Alexander
3. G. Hasinger
4. P. Hopkins
5. F. E. Bauer
6. T. Miyaji
7. L. Hernquist
8. A. Merloni

In Nuclear and High Energy Physics

1. W. N. Brandt
2. G. Hasinger
3. D. M. Alexander
4. T. Miyaji
5. F. E. Bauer
6. A. Merloni
7. A. Comastri
8. P. Hopkins

Citations in the corpus

• Monte Carlo Simulator and Ancillary Response Generator of Suzaku XRT/XIS System for Spatially Extended Source Analysis (2006, methodology): “…would have been difficult without SimASCA and SimARF; e.g., spatial-spectral analysis of clusters of galaxies (Ikebe et al. 1996; Honda et al. 1996), systematic analysis of large volumes of X-ray surveys and the cosmic X-ray background (Ueda et al. 1998; Ueda et al. 1999; Kushino et al. 2002).”
• Reproducibility of Non-X-ray Background for the X-ray Imaging Spectrometer aboard Suzaku (2008, background): “Kushino et al. (2002) measured a CXB power-law photon index of 1.412 and flux of 6.38× 10−8 erg cm−2 s−1 sr−1.”
• Cosmological Evolution of the Hard X-Ray Active Galactic Nucleus Luminosity Function and the Origin of the Hard X-Ray Background (2003, methodology): “As for the absolute CXB intensity we adopt the best-fit value by Kushino et al. (2002), 6.4(±0.7)× 10−8 erg cm−2 s−1 Str−1 in the 2–10 keV band (corresponding to a normalization of 9.7 keV cm−2 s−1 Str−1 keV−1 at 1 keV for a photon index of 1.4), derived from a wide area of 50 deg2 with the ASCA…”
• The synthesis of the cosmic X-ray background in the Chandra and XMM-Newton era (2006, background): “…2004) andChandra (Hickox & Markevitch 2006) as well as a reanalysis of the HEAO1–A2 data (Revnivtsev et al. 2005) have been found to lay in between the original HEAO1–A2 measure and the BeppoSAX one, comparable to those obtained a few years ago by ASCA (Gendreau et al. 1995; Kushino et al. 2002).”
• The Chandra Deep Field North Survey. XIII. 2 Ms Point-Source Catalogs (2003, background): “A photon index of C = 1.4, the slope of the X-ray background in the 0.5–8.0 keV band (e.g., Marshall et al. 1980; Gendreau et al. 1995; Kushino et al. 2002), was assumed in creating the exposure maps.”
• INTEGRAL observations of the cosmic X-ray background in the 5–100 keV range via occultation by the Earth (2006, background): “…(see e.g. Horstman-Moretti et al. 1974; Mazets et al. 1975; Kinzer, Johnson, & Kurfess 1978; Marshall et al. 1980; McCammon et al. 1983; Kinzer et al. 1997; Vecchi et al. 1999; Gruber et al. 1999; Kushino et al. 2002; Lumb et al. 2002; Revnivtsev et al. 2003, 2005; Hickox & Markevitch 2006).”