XTE J1701-462的光谱态：Z源和环礁源之间的联系
Spectral States of XTE J1701-462: Link between Z and Atoll Sources
摘要：
我们分析了2006-2007年吸积中的中子星XTE J1701-462爆发的866个RXTE观测数据，在此期间，源从超爱丁顿光度演化到平静。X射线的颜色演变首先类似于天鹅座X-2的Z源子群，在水平和正常分支（HB/NB）上频繁偏移。然后源衰减并发展到Sco X-1子群，并越来越多地关注于耀斑分支（FB）和“Z”的下顶点。最后，FB消退，并且源转变为环礁源，其中较低的顶点演变为环礁软状态。光谱分析表明，环礁阶段的特点是由一个恒定的内盘半径，而Z阶段表现出一个亮度依赖的扩展的内盘，我们解释为当地的爱丁顿极限相关的影响。与质量吸积率（$\dot{m}$）沿Z方向变化的观点相反，我们发现$\dot{m}$的变化反而是Z和子类长期演化的原因。沿Z分支的运动似乎是由三种不同的机制引起的，它们可能以大致恒定的$\dot{m}$运行。对于斯科X-1-样的Z阶段，我们发现，FB是一个不稳定的轨道，收益的较低的顶点时，内部磁盘半径从设定的值收缩的X射线光度对测量的环礁软状态的值。当边界层的表观尺寸增加而圆盘几乎没有变化时，就会出现NB的偏移。HB与盘发射的康普顿化有关。类天鹅X-2阶段的Z分支更为复杂，其起源尚不清楚。最后，我们的光谱结果使我们假设，较低和较高的Z顶点对应于一个标准的薄磁盘和一个苗条的磁盘，分别。
英文摘要：
We have analyzed 866 RXTE observations of the 2006-2007 outburst of the accreting neutron star XTE J1701-462, during which the source evolves from super-Eddington luminosities to quiescence. The X-ray color evolution first resembles the Cyg X-2 subgroup of Z sources, with frequent excursions on the horizontal and normal branches (HB/NB). The source then decays and evolves to the Sco X-1 subgroup, with increasing focus on the flaring branch (FB) and the lower vertex of the "Z". Finally, the FB subsides, and the source transforms into an atoll source, with the lower vertex evolving to the atoll soft state. Spectral analyses suggest that the atoll stage is characterized by a constant inner disk radius, while the Z stages exhibit a luminosity-dependent expansion of the inner disk, which we interpret as effects related to the local Eddington limit. Contrary to the view that the mass accretion rate ($\dot{m}$) changes along the Z, we find that changes in $\dot{m}$ are instead responsible for the secular evolution of the Z and the subclasses. Motion along the Z branches appears to be caused by three different mechanisms that may operate at roughly constant $\dot{m}$. For the Sco X-1-like Z stage, we find that the FB is an instability track that proceeds off the lower vertex when the inner disk radius shrinks from the value set by the X-ray luminosity toward the value measured for the atoll soft state. Excursions up the NB occur when the apparent size of the boundary layer increases while the disk exhibits little change. The HB is associated with Comptonization of the disk emission. The Z branches for the Cyg X-2-like stage are more complicated, and their origin is unclear. Finally, our spectral results lead us to hypothesize that the lower and upper Z vertices correspond to a standard thin disk and a slim disk, respectively.
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