X-ray binaries are known to launch powerful accretion disk winds that can have a 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 for understanding the wind properties, such as their velocity and ionization, in nearly all cases, we lack the signal-to-noise ratio to constrain the plasma number density, weakening the constraints on the outflow location and mass outflow rate. We present a new approach to determining this number density in the X-ray binary Hercules X-1, by measuring the speed of the wind ionization response to the 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 10¹² 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 ∼3 orders of magnitude in density parameter space, constraining the wind mass outflow rate, energetics, and its launching mechanism.

中文翻译：

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利用其对 X 射线脉动的电离响应来约束 Hercules X-1 吸积盘风的数密度


众所周知，X 射线双星会发射强大的吸积盘风，对双星系统及其周围环境产生重大影响。为了量化影响并确定这些外流的启动机制，我们需要测量风等离子体数密度，这是理论盘风模型的重要组成部分。虽然 X 射线光谱是了解风特性（例如速度和电离）的重要工具，但在几乎所有情况下，我们都缺乏信噪比来约束等离子体数密度，从而削弱了对流出位置的约束和质量流出率。我们提出了一种新方法，通过测量风电离对时变照明连续体的响应速度来确定 X 射线双星 Hercules X-1 中的数密度。 Hercules X-1 由一颗高度磁化的中子星提供动力，脉动周期为 1.24 秒。我们通过使用时间相关光电离模型 tpho 对电离响应进行建模，证明 Hercules X-1 中的风数密度足够高，足以响应这些脉动。然后，我们对 Hercules X-1 的最佳质量 XMM-Newton 观测进行脉冲分辨分析，并直接检测风响应，确认风密度至少为 10 ¹² cm ^-3 。最后，我们模拟了 Hercules X-1 的 XRISM 观测结果，并表明它们将使我们能够准确测量流出物内不同位置的数量密度。通过 XRISM，我们将排除密度参数空间中 ∼3 个数量级，从而约束风团流出速率、能量学及其发射机制。