小质量X射线双星暂现源的暗弱爆发及其吸积物理

We classified the outbursts of low mass X-ray binary transients based on their peak X-ray luminosities. The outbursts with peak luminosities less than 10^37 erg/s are called “faint” outbursts. The outbursts properties are less known than the bright outbursts (peak luminosity > 10^37 erg/s), since the latter are easily discovered by the X-ray all-sky monitors, and are well studied with the follow-up observations. The studies of the “faint” outbursts mainly rely on sensitive X-ray monitoring programs. A large number of such monitoring campaigns were performed during the RXTE and Swift eras, which provide us excellent opportunities to analyze the properties of spectral evolutions and light curves during the “faint” outbursts. We focus on three different kinds of “faint” outburst in this project: low-hard state only outbursts, mini-outbursts and outbursts in very faint X-ray transients. Through the statistical studies of the outburst properties, we are trying to answer two questions related to accretion physics from the observational point of view: 1. What are the mechanisms of different “faint” outbursts and how are they related to the disk instability model? 2. Is there a different accretion flow evolution in the low luminosity regime?

我们依照爆发的峰值光度对小质量X射线双星暂现源的爆发进行分类，其中峰值光度小于10^37 erg/s的爆发称为暗弱爆发。相比于明亮爆发（峰值光度>10^37 erg/s），暗弱爆发的性质了解的不多。因为明亮爆发很容易被全天监测器发现，进而通过后随观测进行细致研究。暗弱爆发的研究则主要依赖于灵敏度较高的监测项目。在RXTE和Swift时代实施了大量的此类监测项目，为我们研究暗弱爆发的能谱演化和光变曲线特征提供了绝佳的机会。本项目中，我们着重研究三种不同类型的暗弱爆发：低硬态爆发，迷你爆发和甚弱X射线暂现源爆发。通过不同类型暗弱爆发特征的统计研究，我们试图从观测角度回答两个和吸积物理相关的问题：1.暗弱爆发的机制是什么？和吸积盘不稳定性模型的关系是怎样？2.低光度下是否存在不同的吸积流演化模式？

在低质量X射线双星暂现源爆发中，峰值光度低于10^37 ergs/s的被称为“暗弱”爆发，由于现在的X射线全天监测设备的灵敏度限制，这种低光度爆发在早期很难被发现，因此它们的爆发性质和演化还并不十分清楚。在本项目中，我们主要依赖灵敏度较高的X射线卫星观测（比如Swift, NuSTAR）和多波段协同观测，研究不同暗弱爆发演化和相应的低光度下吸积物理。我们首次发现在低光度下，黑洞双星冕（热吸积流）的温度和光度成正相关，打破了现有理论模型的预言。我们利用Swift卫星X射线和VLA射电观测，获得了第二例在黑洞暂现源迷你爆发中吸积和喷流的演化过程，关于迷你爆发的研究为该领域带来了新的谜题。我们关于X射线暂现源爆发率和轨道周期的研究结果表明爆发性质不仅和吸积过程有关还和双星的演化历史有关。针对黑洞暂现源中的低硬态爆发，我们也提出了一种可能的理论解释。我们的研究还从恒星级质量黑洞拓展到超大质量黑洞，包括潮汐撕裂恒星事例和“变脸”活动星系核中的爆发/闪耀现象。