Two Different Long-Term Behaviors in Black Hole Candidates: Evidence for Two Accretion Flows?
Two Different Long-Term Behaviors in Black Hole Candidates: Evidence for Two Accretion Flows?
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DOI：
10.1086/339167
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发表时间：
2001-03
期刊：
影响因子：
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通讯作者：
David M. Smith;W. Heindl;J. Swank
中科院分区：
文献类型：
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作者：
David M. Smith;W. Heindl;J. Swank
我们讨论的结果长期硬X射线监测银河系黑洞候选人1 E 1740.7-2942，GRS 1758-258，天鹅座X-1，GX 339-4，和天鹅座X-3与罗西X射线定时探测器。对象分为两类。在第一类中，以天鹅座X-1为例，光度和光谱硬度同时演变。在第二类中，关系更复杂：当计数率下降时出现最软的光谱。大多数为天鹅座X-1量身定做的吸积模型都不能预测第二种行为。一种解释是一个简单的模型，同时有两个独立的吸积流：薄盘和热晕。吸积率的下降会影响两种气流，并会立即通过晕圈传播，但可能需要数周才能通过盘传播。虽然与盘相比，内晕暂时耗尽，但预计会出现暂时的软状态。这张图片得到了观测的支持，即那些显示延迟的源（1 E 1740.7-2942，GRS 1758-258和GX 339-4）预计会有低质量的伴星，而那些不显示延迟的源（天鹅座X-1，天鹅座X-3）则被认为有高质量的伴星。低质量的同伴意味着通过罗氏瓣溢出的吸积，在吸积材料中具有高的比角动量，因此具有长粘性时标的大圆盘。来自大质量伴星的风吸积预计会导致一个小得多的圆盘，因此几乎没有粘性延迟。
We discuss the results of long-term hard X-ray monitoring of Galactic black hole candidates 1E 1740.7-2942, GRS 1758-258, Cyg X-1, GX 339-4, and Cyg X-3 with the Rossi X-Ray Timing Explorer. The objects divide into two classes. In the first class, exemplified by Cyg X-1, luminosity and spectral hardness evolve simultaneously. In the second class, the relation is more complicated: the softest spectra occur while the count rate is dropping. Most models of accretion, tailored to Cyg X-1, do not predict the second sort of behavior. One interpretation is a simple model with two simultaneous, independent accretion flows: a thin disk and a hot halo. A drop in the accretion rate affecting both flows would propagate through the halo immediately but might take up to several weeks to propagate through the disk. While the inner halo is thus temporarily depleted compared to the disk, a temporary soft state is expected. This picture is supported by the observation that those sources that show delays (1E 1740.7-2942, GRS 1758-258, and GX 339-4) are expected to have low-mass companions, and those that do not (Cyg X-1, Cyg X-3) are known or thought to have high-mass companions. Low-mass companions imply accretion by Roche lobe overflow, with a high specific angular momentum in the accreting material, and therefore a large disk with a long viscous timescale. Wind accretion from massive companions is expected to result in a much smaller disk and thus little viscous delay.