利用X射线天文观测鉴别致密星物态

Pulsar-like compact star could be born from the supernovae explosion of massive main sequence star. What is the true equation of state (EoS) of compact stars? Since 1960, it has been one of the most important questions in the research field of nuclear physics and astrophysics. Because of non-perturbation effect of quantum chromodynamics, this question is not yet fully resolved. Theoretically, neutron star and strange star are the possible solutions. The main differences between neutron star and strange star are the predictions of highest and lowest stellar mass, as well as the mass and radius relation. It needs to be tested in astrophysical observations. In our proposal, we will focus on analysing the abundant observational data of low-mass X-ray binaries to search the ultra-low mass compact star, to measure the mass and radius of compact stars from different methods, such as X-ray bursts and quiescent spectra, and then to constrain the EoSs of compact stars. The goals of our proposal are to improve various methods of measuring the mass and radius of compact stars, to check the consistence of different methods, to apply those methods into future observations by Chinese space telescopes, such as HXMT and eXTP, and to cultivate young scientists in X-ray astronomy.

脉冲星类致密天体诞生于大质量恒星演化晚期、超新星爆发过程。这种星体的物态究竟是何？自1960s以来，一直是核物理与天体物理重点研究的问题。但这涉及到量子色动力学的非微扰特性，尚未完全解决。理论上，中子星与奇异星物态模型都是致密星可能的形态。它们之间重要的区别在于预言了截然不同的极限质量（极小与极大质量）与质量—半径关系，需要从天文观测上加以鉴别。在本申请项目中，我们将通过研究低质量X射线双星丰富的辐射现象（X射线暴，宁静态X射线双星等），利用目前积累的大样本X射线观测数据，搜寻小质量的致密星；用不同的方法独立分别独立测量X射线双星中致密星的质量和半径，限制致密物质的状态。本项目的开展，有利于完善和发展各种测量质量和半径的方法，检验不同方法的一致性，并服务于大科学工程HXMT与eXTP，培养和训练X射线天文人才。

致密物质状态与核塌缩型超新星爆发及伴随的核合成与中微子辐射等过程的物理机制、 中子星与恒星级黑洞的质量间隙、双星并合事件发生率、双星并合时辐射引力波的波形等关键问题关联密切。致密星物态的研究在当今天体物理与核物理研究领域都占有关键地位。中子星的 X 射线观测是研究中子星物质状态及其他性质的重要手段。本项目主要通过高能X射线望远镜对中子星低质量X射线双星的观测，测量中子星的质量和半径，限制致密物质状态。具体来说，我们进行了如下研究：（1）分析GRS 1747-312的I型X射线暴，发现了暴的能谱中有吸收边，通过吸收边和光球层膨胀暴，我们测量了GRS 1747-312的引力红移、中子星质量和半径；（2）分析了XMM-Newton和Chandra对Aql X-1的宁静时的观测，拟合宁静态能谱，发现Chandra和XMM-Newton对Aql X-1质量和半径的测量结果一致，我们还利用所有观测数据，给出了Aql X-1的质量和半径的置信区间；（3）分析吸积毫秒脉冲星SAX J1748.9–2021在2015年爆发的观测，分析了X射线暴的性质和态转换的机制；（4）研究了吸积中子星最小磁场。