Isolated Neutron Stars: The Impact of Magnetic Field Decay

孤立的中子星：磁场衰变的影响

• 批准号: 1312822
• 负责人: David Kaplan
• 金额: $ 25.48万
• 依托单位: University of Wisconsin-Milwaukee
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-09-01 至 2017-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1312822&HistoricalAwards=false
• 关键词: Isolated; Neutron; Stars; Impact; Magnetic

Neutron stars are Nature's laboratory for extreme conditions: the high central density probes particle physics in a theoretically intractable regime, and the extreme magnetic fields require the inclusion of quantum electrodynamics. For over two decades, astronomers have attempted to use X-ray observations of neutron star surfaces to measure their radii and cooling rates, as these can strongly constrain the interior structure and properties of the stars. However, the vast majority of the known neutron stars are not ideal for these measurements, as their surfaces are obscured by emission from their magnetic fields (in the cases of rotation-powered pulsars) or by matter orbiting and falling onto their surfaces (in the cases of accretion-powered X-ray binaries). The Isolated Neutron Stars (INSs) are a particular sample of young ( 1 Myr), nearby ( 1 kpc) cooling neutron stars discovered via their soft X-ray emission. They differ from most pulsars in that they have long periods ( 3 s), no radio emission, and X-ray emission that appear to come directly from their surfaces. They are interesting both because of their apparent abundance (comparable to normal pulsars), and because of the promise of inferring neutron star parameters from their thermal emission. However, no consistent interpretation of the thermal emission has emerged, with the difficulty mostly related to their complicated, highly-magnetized atmospheres. Moreover, recent evidence suggests that the magnetic fields we measure now are in fact the results of complicated, non-linear magnetic field decay. Such behavior has been long suspected in neutron stars but never previously observed at this level, and it presents a number of challenges and opportunities. This project will address three broad questions: (1) What is the composition of INS atmospheres, and how can we measure their radii? (2) How important is magnetic field decay to the population of neutron stars inferred from X-ray surveys, and how do their properties compare with those of the population as a whole? (3) Can we constrain the surface magnetic fields (which affect X-ray emission), independent of the dipole fields (which affect timing)? The observations will comprise related radio, optical, and X-ray observations of the INSs and radio pulsars with similar properties. In particular, studies of radio pulsars allow detailed constraints from radio astrometry and polarimetry that are not available for the INSs but will uniquely help us understand their thermal X-ray emission. This work will provide vital clues to a number of outstanding questions in neutron star astrophysics. Only by obtaining consistent results for a number of disparate sources (each with its own peculiarities and systematic uncertainties) will we have robust astrophysical results that can inform the broader physics community.The PI will also continue work with the astronomy club, broadening the range of topics and engaging students in analysis of recent results; recruit undergraduate students for summer projects focusing on specific objects or data-sets, where they will participate in the end-to-end research process; broaden the awareness of and participation in these opportunities through outreach to introductory astronomy classes and other likely interested groups; and assist with the development of shows at the Manfred Olson Planetarium at UWM, which has nearly 10,000 visitors a year. All of these efforts are part of a larger plan to increase the presence of astronomy at UWM through curriculum development, outreach, and mentoring of students from under-represented populations. The PI will also engage in outreach activities with high school students and the general public.

中子星是大自然的极端条件实验室：高中央密度探测理论上棘手的粒子物理，而极端磁场需要包括量子电动力学。二十年来，天文学家一直试图使用中子星表面的X射线观测来测量其半径和冷却速率，因为这些观测可以强烈限制恒星的内部结构和特性。然而，绝大多数已知的中子恒星对于这些测量值并不理想，因为它们的表面被其磁场的发射（在旋转驱动的脉冲星）或轨道上的物质上并落在其表面上（在增生供电的X射线二进制室的情况下）所掩盖。孤立的中子星（INSS）是特定的年轻（1 Myr）样品，附近（1 kpc）冷却中子星通过其软X射线发射发现。它们与大多数脉冲星的不同之处在于，它们的长时间（3 s），没有无线电发射，并且似乎直接来自其表面。它们都很有趣，因为它们的明显丰度（与正常脉冲星相当），并且由于有望从热发射中推断中子星参数。然而，没有出现对热发射的一致解释，这与它们复杂，高度磁性的大气相关的困难。此外，最近的证据表明，我们现在测量的磁场实际上是复杂的，非线性磁场衰减的结果。长期以来，这种行为一直怀疑是中子恒星，但以前从未在这个水平上观察到，并且提出了许多挑战和机遇。该项目将解决三个广泛的问题：（1）INS气氛的组成是什么，我们如何衡量其半径？ （2）磁场衰减对从X射线调查推断的中子星人群的重要性，它们的性质与整个人群的性质如何相比？ （3）我们可以约束表面磁场（影响X射线发射），而与偶极场无关（影响时间）？这些观察结果将包括具有相似特性的INSS和无线电脉冲星的相关无线电，光学和X射线观测值。特别是，对无线电脉冲星的研究允许从射射线标准和极化法进行详细的约束，这些限制无法用于INSS，但会唯一帮助我们理解其热X射线发射。这项工作将为中子星天体物理学中的许多出色问题提供重要线索。只有通过获得许多不同来源（每个人都有其独特性和系统的不确定性）获得一致的结果，我们才能获得强大的天体物理结果，可以为更广泛的物理社区提供信息。招募专注于特定对象或数据集的夏季项目的本科生，他们将参加端到端的研究过程；通过宣传到入门天文学班和其他可能感兴趣的团体来扩大对这些机会的认识和参与；并协助在UWM的Manfred Olson天文馆开发演出，该节目每年有近10,000名游客。所有这些努力都是通过课程开发，外展和指导人群中的学生在UWM增加天文学的更大计划的一部分。 PI还将与高中生和公众进行外展活动。