X-Ray Energy Spectra of the Supersoft X-Ray Sources CAL 87 and RX J0925.7–4758 Observed with ASCA
X-Ray Energy Spectra of the Supersoft X-Ray Sources CAL 87 and RX J0925.7–4758 Observed with ASCA
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使用 ASCA 观测到的超软 X 射线源 CAL 87 和 RX J0925.7–4758 的 X 射线能谱
DOI：
10.1086/319806
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
A. van Teeseling
中科院分区：
文献类型：
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作者：
K. Ebisawa;K. Mukai;T. Kotani;K. Asai;T. Dotani;F. Nagase;H. Hartmann;J. Heise;P. Kahabka;A. van Teeseling
我们报道了用ASCA上的X射线CCD相机(固态成像光谱仪[SISS])对超软X射线源CAL 87和RX J0925.7-4758的观测结果。由于SIS(1keV下ΔE/E~10%)的能量分辨率优于以往的仪器，我们可以首次研究这些源的详细X射线能谱结构。将理论光谱模型应用于CAL87，得到白矮星质量和内禀光度分别为0.8M☉和4×1037-1.2×1038ergs S-1。然而，我们发现观测到的光度比理论估计的要小一个数量级，这表明白矮星被吸积盘永久阻挡，我们正在观测到一个完全电离的吸积盘日冕(ADC)的散射发射，其列密度为~1.5×1023 cm-2。通过模拟，我们已经证明轨道日食可以用ADC模型来解释，即来自ADC的扩展X射线发射的一部分被填充其罗氏叶的伴星所阻挡。我们发现，解释RXJ0925.7-4758的X射线能谱需要很高的表面重力和温度，分别为~1010 cm S-2和~100 eV，以及~1.02keV的强吸收边。这些数值只有在接近钱德拉塞卡极限的极重白矮星上才有可能出现。尽管在Chandrasekhar极限下，RX J0925.7-4758的超软源光度应该是~1038ergs S-1，但观测到的光度要小近两个数量级，即使假设极端距离为~10kpc。为了解释光度差异，我们提出了一个模型，在这个模型中，以前以喷流的形式从系统中喷出的非常厚的物质干扰了视线，由于汤姆森散射而显著降低了光度。
We report observation results of the supersoft X-ray sources CAL 87 and RX J0925.7-4758 with the X-ray CCD cameras (Solid-State Imaging Spectrometers [SISs]) on board ASCA. Because of the superior energy resolution of the SIS (ΔE/E ~ 10% at 1 keV) relative to previous instruments, we could study detailed X-ray spectral structures of these sources for the first time. We have applied theoretical spectral models to CAL 87 and constrained the white dwarf mass and intrinsic luminosity as 0.8-1.2 M☉ and 4 × 1037-1.2 × 1038 ergs s-1, respectively. However, we have found the observed luminosity is an order of magnitude smaller than the theoretical estimate, which indicates that the white dwarf is permanently blocked by the accretion disk, and we are observing a scattering emission by a fully ionized accretion disk corona (ADC) whose column density is ~1.5 × 1023 cm-2. Through simulation we have shown that the orbital eclipse can be explained by the ADC model, such that a part of the extended X-ray emission from the ADC is blocked by the companion star filling its Roche lobe. We have found that very high surface gravity and temperature, ~1010 cm s-2 and ~100 eV, respectively, as well as a strong absorption edge at ~1.02 keV, are required to explain the X-ray energy spectrum of RX J0925.7-4758. These values are only possible for an extremely heavy white dwarf near the Chandrasekhar limit. Although the supersoft source luminosity should be ~1038 ergs s-1 at the Chandrasekhar limit, the observed luminosity of RX J0925.7-4758 is nearly 2 orders of magnitude smaller, even assuming an extreme distance of ~10 kpc. To explain the luminosity discrepancy, we propose a model in which very thick matter that was previously ejected from the system, as a form of jets, intervenes the line of sight and reduces the luminosity significantly because of Thomson scattering.