Absolute Measurement of the Unresolved Cosmic X-ray Background in the 0.5–8 Kev Band with Chandra
نویسنده
چکیده
We present the absolute measurement of the unresolved 0.5–8 keV cosmic X-ray background (CXB) in the Chandra Deep Fields (CDFs) North and South, the longest observations with Chandra (2 Ms and 1 Ms, respectively). We measure the unresolved CXB intensity by extracting spectra of the sky, removing all point and extended sources detected in the CDF. To model and subtract the instrumental background, we use observations obtained with ACIS in stowed position, not exposed to the sky. The unresolved signal in the 0.5–1 keV band is dominated by diffuse Galactic and local thermal-like emission. We find unresolved intensites in the 0.5–1 keV band of (4.1 ± 0.3) × 10 ergs cm s deg for CDF-N and (5.0± 0.4)× 10 for CDF-S. In the 1–8 keV band, the unresolved spectrum is adequately described by a power law with a photon index Γ = 1.5 −0.4 and normalization 2.6± 0.3 photons cm s keV sr at 1 keV. We find unresolved CXB intensities of (1.04± 0.14)× 10 ergs cm s deg for the 1–2 keV band and (3.4 ± 1.7) × 10 ergs cm s deg for the 2–8 keV band. Our detected unresolved intensities in these bands significantly exceed the expected flux from sources below the CDF detection limits, if one extrapolates the logN/ logS curve to zero flux. Thus these background intensities imply either a genuine diffuse component, or a steepening of the logN/ logS curve at low fluxes, most significantly for energies <2 keV. Adding the unresolved intensity to the total contribution from sources detected in these fields and wider-field surveys, we obtain a total intensity of the extragalactic CXB of (4.6± 0.3)× 10 ergs cm s deg for 1–2 keV and (1.7±0.2)×10 ergs cm s deg for 2–8 keV. These totals correspond to a CXB power law normalization (for Γ = 1.4) of 10.9 photons cm s keV sr at 1 keV. This corresponds to resolved fracations of 77± 3% and 80± 8% for 1–2 and 2–8 keV, respectively. Subject headings: galaxies: active — methods: data analysis — X-rays: diffuse background — X-rays: galaxies
منابع مشابه
Absolute Measurement of the Unresolved X-ray Background in the 0.5–8 Kev Band with Chandra
We present the absolute measurement of the unresolved 0.5–8 keV X-ray background in the Chandra Deep Fields (CDF) North and South, the longest observations with Chandra (2 Ms and 1 Ms, respectively). We measure the unresolved CXB intensity by extracting spectra of the sky, removing all point and extended sources detected in the CDF. To model and subtract the instrumental background, we use obse...
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