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arXiv 1306.1570astro-ph.HE
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银河系黑洞X射线双星的X射线光谱向静止演化

The X-ray Spectral Evolution of Galactic Black Hole X-ray Binaries Toward Quiescence

Richard M. Plotkin, Elena Gallo, Peter G. Jonker

摘要:

大多数瞬变黑洞X射线双星(BHXB)大部分时间处于静止状态,它们以高度亚爱丁顿光度从伴星吸积物质(我们在这里将静止定义为标准化的爱丁顿比l_x = L_{0.5-10 keV} }/ L_{Edd} <1 e-5)。在这里,我们提出了钱德拉X射线成像光谱的三个BHXB系统(H 1743-322,MAXI J1659-152,和XTE J1752-223),因为他们陷入平静后爆发。在一个月内进行了多次X射线观测,使我们能够跟踪每个系统在衰变期间的X射线光谱演变。我们比较这三个系统与其他BHXB系统。我们证实,静态BHXB具有软X射线光谱比低硬态BHXB,静态BHXB光谱特性不依赖于二元系统的轨道参数。然而,观察到的X射线光子指数和l_x之间的反相关在低硬态不继续一旦BHXB进入静止。相反,当l_x达到约1 e-5时,光子指数稳定在2.08+/-0.07的平均值。因此,Lx ~ 1 e-5是静态光谱状态开始时的观测激发上限。我们的结果进行了讨论的背景下,不同的吸积流模型,并在整个黑洞质量尺度。

英文摘要:

Most transient black hole X-ray binaries (BHXBs) spend the bulk of their time in a quiescent state, where they accrete matter from their companion star at highly sub-Eddington luminosities (we define quiescence here as a normalized Eddington ratio l_x = L_{0.5-10 keV}}/L_{Edd} < 1e-5). Here, we present Chandra X-ray imaging spectroscopy for three BHXB systems (H 1743-322, MAXI J1659-152, and XTE J1752-223) as they fade into quiescence following an outburst. Multiple X-ray observations were taken within one month of each other, allowing us to track each individual system's X-ray spectral evolution during its decay. We compare these three systems to other BHXB systems. We confirm that quiescent BHXBs have softer X-ray spectra than low-hard state BHXBs, and that quiescent BHXB spectral properties show no dependence on the binary system's orbital parameters. However, the observed anti-correlation between X-ray photon index and l_x in the low-hard state does not continue once a BHXB enters quiescence. Instead, the photon index plateaus to an average value of 2.08+/-0.07 by the time l_x reaches approximately 1e-5. l_x~1e-5 is thus an observationally-motivated upper limit for the beginning of the quiescent spectral state. Our results are discussed in the context of different accretion flow models, and across the black hole mass scale.

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