“慧眼”HXMT对中子星低质量X射线双星的观测研究

Neutron star Low-mass X-ray binary (NS-LMXB) was the first X-ray source discovered outside the solar system. NS-LMXBs provide us an ideal laboratory to study the accretion process and accretion disc theory, the equation of state of dense matter and general relativistic effects in the ultra-strong gravity regime. The understanding of NS-LMXBs comes mainly from the spectral and timing observations of X-ray telescopes. Until now, many open questions are needed to be clarified, such as the origin of low frequency quasi-periodic oscillation (QPO), the behaviors of broad band emission, the mechanism of spectral transition, and the equation of state of neutron star. The solutions of these questions can be promoted by insight-HXMT, which has broad band spectral detectors with good energy resolution, high timing resolution and large effective area. In this application, by using high statistical observations with insight-HXMT, we will analyze the timing and spectra of neutron star low-mass X-ray binaries. From the observations, we will research broad-band spectra of LMXBs, test the theory of low frequency QPO, i.e., Lense-Thirring effect, evaluate the neutron star iron line, determine the gravitational redshift with the absorption edge and measure the neutron star mass and radius from type-I X-ray bursts to constrain the neutron star equations of state. We expect that the insight-HXMT observations will make a great contribution to the studies of neutron star low-mass X-ray binaries.

中子星低质量X射线双星（LMXB）是人类发现的第一个太阳系外的X射线源，它们是研究吸积盘理论、极端致密物质状态和强引力场下的广义相对论效应等基本物理问题的理想实验室。人们对中子星LMXB的认识主要来自于空间望远镜能谱和时变观测，目前还有很多问题尚未澄清，例如低频准周期震荡的起源、宽能段辐射行为、谱态演化机制、中子星物质状态等。“慧眼”-HXMT卫星具有宽能段、良好能量分辨率、高时间分辨、大有效面积等特点，在运行期间将推动或解决这些问题。本课题将依据“慧眼”-HXMT卫星对中子星LMXB时变与能谱的高统计量观测，进行以下研究：研究中子星LMXB宽能段辐射行为；检验低频QPO的Lense-Thirring理论模型；系统地测量中子星的Fe发射线；从X射线暴中，通过吸收边测量中子星表面引力红移、中子星的质量和半径，限制致密物质状态。我们期待“慧眼”望远镜观测对中子星LMXB研究做出重要贡献。

中子星的 X 射线观测是研究致密天体吸积过程的重要手段。本项目主要通过慧眼硬X射线调制望远镜等高能X射线望远镜对中子星低质量X射线双星的观测，研究了I型X射线暴、低质量X射线双星的宽能段辐射、吸积毫秒脉冲星的脉冲特征，具体来说，我们进行了如下研究：（1）分析4U 1636-536和4U 1730-22的I型X射线暴，研究了暴与吸积盘的相互作用；（2）发现了4U 1730-22的585 Hz的暴频；（3）分析吸积毫秒脉冲星Swift J1756.9-2508在2018年和2019爆发的观测，分析了X射线脉冲的脉冲轮廓、周期演化等性质；（4）研究了吸积中子星最小磁场等。在项目资助期间，共发表论文17篇，培养多名研究生。