利用 Hercules X-1 对X射线脉冲的电离响应约束其吸积盘风的数密度
Constraining the Number Density of the Accretion Disk Wind in Hercules X-1 Using its Ionization Response to X-ray Pulsations
AI总结：
本研究提出利用X射线脉冲电离响应测量吸积盘风数密度的新方法，在Hercules X-1中证实风密度至少为$10^{12}$ cm$^{-3}$，并预测XRISM观测可进一步约束其外流参数与抛射机制。
摘要：
X射线双星会抛射强劲的吸积盘风，这类风能够对双星系统及其周围环境产生显著影响。为量化这些外流的影响并确定其抛射机制，我们需要测量风等离子体的数密度，这是理论盘风模型中的一个重要参数。尽管X射线光谱学是研究风的性质（如速度和电离度）的关键工具，但在几乎所有情况下，我们都缺乏足够的信噪比来约束等离子体数密度，这削弱了对外流位置和质量外流率的约束。\n我们提出了一种新方法，通过测量风的电离对时变照射连续谱的响应速度，来确定X射线双星Hercules X-1中的这一数密度。Hercules X-1由一颗高度磁化的中子星供能，脉冲周期为1.24秒。我们通过使用时间相关光致电离模型TPHO对电离响应进行建模，证明Hercules X-1中的风数密度足够高，能够对这些脉冲产生响应。随后我们对Hercules X-1质量最高的XMM-牛顿观测数据进行了脉冲分辨分析，直接探测到了风的响应，证实风的密度至少为$10^{12}$ cm$^{-3}$。最后，我们模拟了XRISM对Hercules X-1的观测，结果表明这些观测将使我们能够精确测量外流内部不同位置的数密度。借助XRISM，我们将能排除约3个数量级的密度参数空间，从而约束风的质量外流率、能量学特性及其抛射机制。
英文摘要：
X-ray binaries are known to launch powerful accretion disk winds that can have significant impact on the binary systems and their surroundings. To quantify the impact and determine the launching mechanisms of these outflows, we need to measure the wind plasma number density, an important ingredient in the theoretical disk wind models. While X-ray spectroscopy is a crucial tool to understanding the wind properties, such as their velocity and ionization, in nearly all cases, we lack the signal-to-noise to constrain the plasma number density, weakening the constraints on outflow location and mass outflow rate. We present a new approach to determine this number density in the X-ray binary Hercules X-1 by measuring the speed of the wind ionization response to time-variable illuminating continuum. Hercules X-1 is powered by a highly magnetized neutron star, pulsating with a period of 1.24 s. We show that the wind number density in Hercules X-1 is sufficiently high to respond to these pulsations by modeling the ionization response with the time-dependent photoionization model TPHO. We then perform a pulse-resolved analysis of the best-quality XMM-Newton observation of Hercules X-1 and directly detect the wind response, confirming that the wind density is at least $10^{12}$ cm$^{-3}$. Finally, we simulate XRISM observations of Hercules X-1 and show that they will allow us to accurately measure the number density at different locations within the outflow. With XRISM we will rule out $\sim3$ orders of magnitude in density parameter space, constraining the wind mass outflow rate, energetics, and its launching mechanism.
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