指环王：从巨大的X射线光回波到Circinus X-1的运动学距离
Lord of the Rings: A Kinematic Distance to Circinus X-1 from a Giant X-Ray Light Echo
摘要：
Circinus X-1在2013年末展示了一个明亮的X射线耀斑。钱德拉和XMM-牛顿在耀斑发生后40至80天的后续观测显示，有一个明亮的X射线光回波，其形式为四个定义明确的环，半径从5到13弧分，半径随时间增长。耀斑的巨大能量密度和圆规座X-1上星际尘埃的巨大柱状密度使其成为迄今为止观测到的最大和最明亮的X射线光回波环。通过反卷积的径向强度轮廓的回波与MAXI X射线光变曲线的耀斑，我们重建的尘埃分布对Circinus X-1到四个不同的尘埃浓度。通过比较散射强度峰值与Mopra南银道面CO巡天分子云CO图中的峰值强度，我们确定了两个最里面的环，云的径向速度分别为~ -74 km/s和~ -81 km/s。我们确定了一个突出的前景光电吸收带的CO气体在~ -32公里/秒的车道。根据这些光环与单个CO云的联系，我们确定了到圆规座X-1的运动学距离为$D_{Cir X-1} = 9.4^{+0.8}_{-1.0}$ kpc。这一距离排除了之前关于距离约为4 kpc的说法，意味着圆规座X-1是一个频繁的超爱丁顿源，并将洛伦兹因子的下限设定为PDMATHAMN，喷流视角的上限设定为$θ_{jet} \lesssim 3^{\circ}$。
英文摘要：
Circinus X-1 exhibited a bright X-ray flare in late 2013. Follow-up observations with Chandra and XMM-Newton from 40 to 80 days after the flare reveal a bright X-ray light echo in the form of four well-defined rings with radii from 5 to 13 arcminutes, growing in radius with time. The large fluence of the flare and the large column density of interstellar dust towards Circinus X-1 make this the largest and brightest set of rings from an X-ray light echo observed to date. By deconvolving the radial intensity profile of the echo with the MAXI X-ray lightcurve of the flare we reconstruct the dust distribution towards Circinus X-1 into four distinct dust concentrations. By comparing the peak in scattering intensity with the peak intensity in CO maps of molecular clouds from the Mopra Southern Galactic Plane CO Survey we identify the two innermost rings with clouds at radial velocity ~ -74 km/s and ~ -81 km/s, respectively. We identify a prominent band of foreground photoelectric absorption with a lane of CO gas at ~ -32 km/s. From the association of the rings with individual CO clouds we determine the kinematic distance to Circinus X-1 to be $D_{Cir X-1} = 9.4^{+0.8}_{-1.0}$ kpc. This distance rules out earlier claims of a distance around 4 kpc, implies that Circinus X-1 is a frequent super-Eddington source, and places a lower limit of $Γ\gtrsim 22$ on the Lorentz factor and an upper limit of $θ_{jet} \lesssim 3^{\circ}$ on the jet viewing angle.
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