利用低质量X射线双星种群合成研究低质量间隙
Investigating the Lower Mass Gap with Low Mass X-ray Binary Population Synthesis
AI总结：
本研究通过种群合成模拟与双星演化模型，定量分析瞬变低质量X射线双星的选择偏差对质量间隙黑洞观测的影响，发现吸积诱发坍缩形成的质量间隙黑洞种群与观测不符，提出需补充相关物理机制以解释低质量黑洞的观测缺失。
AI中文摘要：
来自低质量黑洞X射线双星（LMXBs）和射电脉冲星的质量测量已被用于识别大质量中子星（NSs）与小质量黑洞（BHs）之间的质量间隙。LMXBs中的黑洞质量测量通常仅对瞬变系统可行：爆发期可通过全天X射线监测器实现探测，而宁静期则可对低质量伴星进行视向速度测量。我们定量研究了因黑洞质量测量需瞬变行为这一要求带来的选择偏差。通过快速种群合成模拟（COSMIC）、详细的双星恒星演化模型（MESA）以及瞬变行为的盘不稳定性模型，我们证明瞬变LMXB选择效应会引入观测偏差，并可能导致观测样本中质量间隙黑洞被抑制。然而，我们发现一类包含质量间隙黑洞的瞬变LMXB种群，是通过LMXB阶段内中子星的吸积诱发坍缩形成的，这与观测结果不符。这些结果在双星演化 prescriptions 变化的情况下仍具稳健性。该吸积诱发坍缩种群的重要性取决于中子星诞生最大质量$M_\text{ NS, birth-max}$。为反映观测到的低质量黑洞匮乏现象，COSMIC和MESA模型更支持$M_\text{ NS, birth-max} \lesssim2M_{\odot}$。在不存在针对含质量间隙黑洞的LMXB的其他观测偏差的情况下，我们的结果表明，LMXB形成与演化建模需要引入额外的物理机制。
英文摘要：
Mass measurements from low-mass black hole X-ray binaries (LMXBs) and radio pulsars have been used to identify a gap between the most massive neutron stars (NSs) and the least massive black holes (BHs). BH mass measurements in LMXBs are typically only possible for transient systems: outburst periods enable detection via all-sky X-ray monitors, while quiescent periods enable radial-velocity measurements of the low-mass donor. We quantitatively study selection biases due to the requirement of transient behavior for BH mass measurements. Using rapid population synthesis simulations (COSMIC), detailed binary stellar-evolution models (MESA), and the disk instability model of transient behavior, we demonstrate that transient-LMXB selection effects introduce observational biases, and can suppress mass-gap BHs in the observed sample. However, we find a population of transient LMXBs with mass-gap BHs form through accretion-induced collapse of a NS during the LMXB phase, which is inconsistent with observations. These results are robust against variations of binary evolution prescriptions. The significance of this accretion-induced collapse population depends upon the maximum NS birth mass $M_\mathrm{ NS, birth-max}$. To reflect the observed dearth of low-mass BHs, COSMIC and MESA models favor $M_\mathrm{ NS, birth-max} \lesssim2M_{\odot}$. In the absence of further observational biases against LMXBs with mass-gap BHs, our results indicate the need for additional physics connected to the modeling of LMXB formation and evolution.
