2015年黑洞X射线双星V404 Cygni的衰变：鲁棒的喷流-喷流耦合和急剧过渡到静止
The 2015 Decay of the Black Hole X-ray Binary V404 Cygni: Robust Disk-Jet Coupling and a Sharp Transition into Quiescence
摘要：
我们在2015年爆发结束时同时对黑洞X射线双星V404 Cygni进行了X射线和无线电观测。从2015年7月11日到8月5日，我们用Chandra，Swift和NuSTAR在X射线中监测了V404 Cygni，并用Karl G. Jansky甚大阵和甚长基线阵在射电中的位置，覆盖了1989年爆发时覆盖不好的光度范围（我们2015年的活动覆盖了2 e33 <Lx<1 e34 erg/s）。在我们2015年的活动中，X射线光谱从γ ~1.6（Lx~ 1 e34 erg/s）的硬光子指数迅速发展到γ ~2（Lx~ 3e 33 erg/s）的软光子指数。我们认为，V404天鹅座达到伽玛~2标志着开始的静态光谱状态，这发生在一个高的X射线光度比平均爆发前的光度~ 8 e32 erg/s的3-4倍。天鹅座V404的射电/X射线光度相关性与它在1989年的前一次爆发相同，这意味着它有一个强大的盘-喷流耦合。我们排除的可能性，同步加速器冷却射流占主导地位的X射线发射在静止，离开同步加速器自康普顿从热吸积流或从辐射冷却射流作为最有可能的来源X射线辐射，和/或粒子加速沿射流变得不那么有效的静止。最后，我们提出了第一个迹象的相关无线电和X射线的变化在分钟的时间尺度上的平静，暂时测量无线电发射滞后X射线15+/-4分钟，这表明X射线的变化传播下来的喷流长度<3.0 AU。
英文摘要：
We present simultaneous X-ray and radio observations of the black hole X-ray binary V404 Cygni at the end of its 2015 outburst. From 2015 July 11-August 5 we monitored V404 Cygni with Chandra, Swift, and NuSTAR in the X-ray, and with the Karl G. Jansky Very Large Array and the Very Long Baseline Array in the radio, spanning a range of luminosities that were poorly covered during its previous outburst in 1989 (our 2015 campaign covers 2e33<Lx<1e34 erg/s). During our 2015 campaign, the X-ray spectrum evolved rapidly from a hard photon index of Gamma~1.6 (at Lx~1e34 erg/s) to a softer Gamma~2 (at Lx~3e33 erg/s). We argue that V404 Cygni reaching Gamma~2 marks the beginning of the quiescent spectral state, which occurs at a factor of ~3-4 higher X-ray luminosity than the average pre-outburst luminosity of ~8e32 erg/s. V404 Cygni falls along the same radio/X-ray luminosity correlation that it followed during its previous outburst in 1989, implying a robust disk-jet coupling. We exclude the possibility that a synchrotron cooled jet dominates the X-ray emission in quiescence, leaving synchrotron self-Compton from either a hot accretion flow or from a radiatively cooled jet as the most likely sources of X-ray radiation, and/or particle acceleration along the jet becoming less efficient in quiescence. Finally, we present the first indications of correlated radio and X-ray variability on minute timescales in quiescence, tentatively measuring the radio emission to lag the X-ray by 15+/-4 min, suggestive of X-ray variations propagating down a jet of length <3.0 AU.
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