A new census of globular cluster pulsars

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。邓肯洛里默博士和合作者将进行详细的统计研究的中子星星人口的球状星团的银河系。 球状星团所提供的稠密恒星环境就像是天体物理实验室，用来探测恒星演化和双星与多星星系统的动力学。球状星团中的中子星是星团中完整星星形成历史的长寿命示踪剂，具有丰富的物理应用。射电脉冲星--快速旋转的高磁化中子星--为了解这一群体提供了一个非常强大的窗口。例如，对射电双星的计时观测首次证明了球状星团中存在电离气体，并为大质量中子星的存在提供了最新证据，这对许多超密度物质的状态方程提出了挑战。球状星团未来的发现包括毫秒射电双星和脉冲星-黑洞双星系统。目前，在26个球状星团中已知有140个射电双星。这些发现中大约有一半是在过去五年中由西弗吉尼亚州国家科学基金会资助的绿色银行望远镜的小组发现的。尽管取得了这些重大进展，但对球状星团中射电脉冲星种群的最后一次大规模普查是在15年前进行的，当时在少数星团中已知的天体不到20多个。当时，尚不清楚毫秒双星（低质量X射线双星）的祖先是否足以解释银河系球状星团中疑似存在的10，000颗毫秒双星。Lorimer博士计划对种群进行全面的新分析，以考虑由于双星运动，星际传播和无线电频率干扰而产生的选择效应。他的团队在脉冲星观测和人口建模方面有着广泛的经验，这些经验是开发球状星团中射电星基本人口的详细蒙特卡罗模型所必需的。除了描述球状星团中射电星的总体大小和出生率外，他们将应用频率论和贝叶斯统计分析来确定旋转周期的基本分布，光度和（对于双星系统）轨道参数。他们还将解决已知存在于球状星团中的较年轻的双星的较小子集，以及由于引力辐射的发射而将在亚哈勃时间尺度上合并的双星。这些结果有望为基于恒星演化模型的中子星星种群补充研究提供重要的投入。他们还将帮助确定作为引力波源的致密天体双星的可能数量。拟议中的研究将影响其他一些领域，这将有利于西弗吉尼亚州，教授天文学课程和天文学研究。具体而言，首席研究员及其团队将：（a）为天文学本科生开发一个可免费使用的实验室组件;（B）为高中理科教师及其学生开发一个探究式学习工具;（c）提升西弗吉尼亚大学的国际研究形象，帮助增加科学、技术、工程和数学学科的学生人数;（d）加强未来国家和国际无线电设施的科学案例;（e）提供一个开放源码工具库，用于天文群体的蒙特卡罗模拟。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Dr. Duncan Lorimer and collaborators will undertake a detailed statistical study of the neutron star population in the globular clusters of the Milky Way Galaxy. The dense stellar environments provided by globular clusters act as astrophysical laboratories to probe stellar evolution and the dynamics of binary and multiple star systems. Neutron stars in globular clusters are long-lived tracers of the integrated star formation history in clusters and have a wealth of physical applications. Radio pulsars - rapidly spinning highly magnetized neutron stars - provide a very powerful window into this population. Timing observations of radio pulsars, for example, have demonstrated for the first time the existence of ionized gas in globular clusters and provide recent evidence for the existence of high-mass neutron stars which challenge many equations of state for super-dense matter. Future discoveries expected from globular clusters include binary pairs of millisecond pulsars and pulsar-black hole binary systems.Currently, 140 radio pulsars are known in 26 globular clusters. Around half of these discoveries have been made in the past five years by groups using the NSF-funded Green Bank Telescope in West Virginia. Despite these significant advances, the last major census of the radio pulsar population in globular clusters was carried out over 15 years ago when less than two-dozen objects were known in a handful of clusters. At that time, it was not clear whether the progenitor population of millisecond pulsars (the low-mass X-ray binaries) was sufficient to account for the estimated number of 10,000 pulsars suspected to exist in the Galactic globular cluster population. Dr. Lorimer plans a comprehensive new analysis of the population to take account of selection effects due to binary motion, interstellar propagation and radio frequency interference. His team has a broad range of experience in pulsar observations and population modeling necessary to develop detailed Monte Carlo models of the underlying population of radio pulsars in globular clusters.In addition to characterizing the overall size and birth-rate of radio pulsars in globular clusters, they will apply both frequentist and Bayesian statistical analyses to determine the underlying distributions of spin period, luminosity and (for binary systems) orbital parameters. They will also address the smaller subset of younger pulsars known to exist in globular clusters, and those binaries which will merge on sub-Hubble timescales due to the emission of gravitational radiation. These results are expected to provide vital input to complementary studies of the neutron star population which are based on models of stellar evolution. They will also help determine the likely size of the population of compact object binaries that contribute as gravitational-wave sources.The proposed research will impact upon a number of other areas which will benefit the state of West Virginia, teaching astronomy courses and astronomical research in general. Specifically, the PI and his team will (a) develop a freely-available laboratory component for undergraduate astronomy students; (b) develop an inquiry-based learning tool for high-school science teachers and their students; (c) raise the international research profile of West Virginia University and help to increase the number of students in Science, Technology, Engineering and Mathematics disciplines; (d) enhance the science case for future national and international radio facilities; (e) make available an open-source library of tools for Monte Carlo simulations of astronomical populations.