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首页> 外文期刊>The Astrophysical journal >ABSOLUTE MEASUREMENT OF THE UNRESOLVED COSMIC X-RAY BACKGROUND IN THE 0.5-8 keV BAND WITH CHANDRA
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ABSOLUTE MEASUREMENT OF THE UNRESOLVED COSMIC X-RAY BACKGROUND IN THE 0.5-8 keV BAND WITH CHANDRA

机译：带有CHANDRA的0.5-8 keV波段绝对分辨的宇宙X射线背景的绝对测量

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摘要

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 and 1 Ms, respectively). We measure the unresolved CXB intensity by extracting spectra of the sky and 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) x 10~(-12) ergs cm~(-2) s~(-1) deg~(-2) for CDF-N and (5.0 ± 0.4) x 10~(-12) 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)~(+0.5) and normalization 2.6 ± 0.3 photons s~(-1) keV~(-1) sr~(-1) at 1 keV. We find unresolved CXB intensities of (1.04 ± 0.14) x 10~(-12) ergs cm~(-2) s~(-1) deg~(-2) for the 1-2 keV band and (3.4 ± 1.7) x 10~(-12) ergs cm~(-2) s~(-1) deg~(-2) 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 log N/log S curve to zero flux. Thus, these background intensities imply either a genuine diffuse component or a steepening of the log N/log S 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) x 10~(-12) ergs cm~(-2) s~(-1) deg~(-2) for 1-2 keV and (1.7 ± 0.2) x 10~(-11) ergs cm~(-2) s~(-1) deg~(-2) for 2-8 keV. These totals correspond to a CXB power-law normalization (for Γ = 1.4) of 10.9 photons cm~(-2) s~(-1) keV~(-1) sr~(-1) at 1 keV. This corresponds to resolved fractions of 77% ± 3% and 80% ± 8% for 1-2 and 2-8 keV, respectively.
机译：我们介绍了在钱德拉深场（CDFs）北部和南部未分辨的0.5-8 keV宇宙X射线背景（CXB）的绝对测量，这是用钱德拉（2和1 Ms）最长的观测时间。我们通过提取天空光谱并去除CD​​F中检测到的所有点和扩展源来测量未解决的CXB强度。为了对仪器的背景进行建模和减去，我们使用了ACIS在收起位置且未暴露于天空的情况下获得的观测值。 0.5-1 keV频带中未解析的信号主要由扩散银河和类似局部热的发射所控制。对于CDF-N和（5.0），我们在（4.1±0.3）x 10〜（-12）ergs cm〜（-2）s〜（-1）deg〜（-2）的0.5-1 keV带中发现了未解析的强度。 CDF-S为±0.4）x 10〜（-12）在1-8 keV波段中，未分解谱由光子指数Γ= 1.5 _（-0.4）〜（+0.5）和归一化2.6±0.3光子s〜（-1）keV〜（ -1）在1 keV时sr〜（-1）。我们发现1-2 keV波段和（3.4±1.7）的（1.04±0.14）x 10〜（-12）ergs cm〜（-2）s〜（-1）deg〜（-2）的未解析CXB强度对于2-8 keV波段x 10〜（-12）ergs cm〜（-2）s〜（-1）deg〜（-2）。如果将对数N / log S曲线外推至零通量，则我们在这些谱带中检测到的未解析强度大大超过了低于CDF检测极限的光源预期通量。因此，这些背景强度意味着在低通量下真正的扩散成分或log N / log S曲线变陡，对于能量<2 keV而言最明显。将未解决的强度加上这些领域和更广泛的现场调查中发现的源的总贡献，我们得出的河外CXB的总强度为（4.6±0.3）x 10〜（-12）ergs cm〜（-2）s〜 1-2 keV时为（-1）deg〜（-2），2-时为（1.7±0.2）x 10〜（-11）ergs cm〜（-2）s〜（-1）deg〜（-2） 8 keV。这些总数对应于1 keV处的10.9个光子cm〜（-2）s〜（-1）keV〜（-1）sr〜（-1）的CXB幂律归一化（对于Γ= 1.4）。这对应于1-2和2-8 keV的分辨分数分别为77％±3％和80％±8％。

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