RUI: Detecting Gravitational Waves with Pulsars: Mitigating the ISM Delay

脉冲星计时可以用来探索引力和恒星物理的许多方面。特别是，脉冲星可以通过监测脉冲的到达时间来搜索引力波--由黑洞等大质量加速引起的时空涟漪。这种长期的合作努力是现代物理学和天体物理学的伟大探索之一。所采用的技术对波长为光年的引力波很敏感，例如，在合并星系的核心绕着超大质量黑洞运行时产生的引力波。这种波长机制不能用其他技术探测，例如LIGO和拟议的LISA任务正在探索的那些技术。通过不均匀星际气体的多路径传播--以及随后的干扰效应--导致无线电信号的强度或闪烁程度不同。闪烁效应通过在计时信号中引入随机噪声，阻碍了脉冲星的高精度计时。所需的计时精度是非同寻常的：大约维持了100 ns。PI和他的奥伯林大学本科生正在开发一种技术，可以从脉冲星的时变频谱中估计出小于一微秒的时间延迟。尽管在这项技术上需要做很多开发工作，但初步结果是有希望的，并强调了理解和纠正这种延迟的重要性。拟议的研究将利用阿雷西博射电望远镜和其他大型望远镜，如NRAO/Green Bank望远镜和欧洲正在组织的LEAP(虚拟阵列)望远镜的高灵敏度观测，详细开发这项技术。主要目标是关注这一重要的定时噪声来源，并开发一种实用的技术来修正相对较弱的毫秒脉冲的定时信号。这项研究将通过提高我们用毫秒脉冲星阵列探测引力波的能力而造福于科学界。此外，我们对银河系中电离气体对无线电波散射的了解将有助于我们更好地理解银河系是如何工作的，例如星际气体的湍流程度就是它在太空中的分布方式。这两个主题不仅对专家感兴趣，而且对更广泛的受众也很感兴趣。作为一名文理学院的教授，PI与他的研究学生和他所教的广泛的学生分享了这项工作的兴奋之情。例如，他每年向大约100名本科生教授天文学入门课程，直接受益于他对科学研究的参与。这项研究计划将让本科生兴奋地探索一种新的现象，并拼凑出一个更大的谜题的部分。通过与PI及其合作者的密切合作，学生将获得广泛的技术技能，并进一步发展他们独立探索问题的能力。使用世界上最大的射电望远镜的最先进的电子和计算机，学生将获得信心，他们有能力解决大型和复杂的问题。有机会与美国和国外的科学家合作，并在会议和出版物上报告他们的工作，将增强学生的研究经验，并为他们接受研究生培训或在技术劳动力中担任其他角色做好准备。

Pulsar timing can be used to explore many aspects of gravitation and stellar physics. In particular, pulsars can be used to search for gravitational waves - ripples in space-time caused by the acceleration of large masses such as black holes - by monitoring the arrival time of the pulses. This long-term, collaborative effort is one of the great quests of modern physics and astrophysics. The technique employed is sensitive to gravitational waves with light-year wavelengths produced, for example, by orbiting supermassive black holes at the cores of merging galaxies. This wavelength regime cannot be probed by other techniques, for example those being explored by LIGO and the proposed LISA mission. Multi-path propagation through the inhomogeneous interstellar gas - and subsequent interference effects - causes the radio signal to vary in strength or scintillate. Scintillation effects hamper high precision timing of pulsars by introducing random noise into the timing signal. The required timing precision is extraordinary: about 100 ns maintained for years.The PI and his Oberlin College undergraduate students are developing a technique that allows time delays smaller than a microsecond to be estimated from the time-variable spectrum of the pulsar. Although there is much development work needed on this technique, initial results are promising and underscore the importance of understanding and correcting for this delay. The proposed research will develop this technique in detail using high-sensitivity observations from the Arecibo radio telescope and other large telescopes such as the NRAO/Green Bank Telescope and the LEAP (virtual array) telescope being organized in Europe. The main goal is to focus on this important source of timing noise and develop a practical technique for correcting for it in the timing signal of relatively weak millisecond pulsars.This research will benefit the scientific community by improving our ability to detect gravitational waves with an array of millisecond pulsars. In addition, what we learn about scattering of radio waves by the ionized gas in the Milky Way will improve our understanding of how the Milky Way "works," for example the degree of turbulence of the interstellar gas is how it is distributed in space. Both of these topics are of interest not only to specialists, but to a much wider audience as well. As a professor at a liberal arts college, the PI shares the excitement of this work with his research students and with the wide range of students he teaches. His teaching of Introductory Astronomy to about 100 undergraduates a year, for example, benefits directly from his involvement in scientific research. This research program will involve undergraduate students in the excitement of exploring a new phenomenon and piecing together parts of a bigger puzzle. By working closely with the PI and his collaborators, the students will gain a broad range of technical skills as well as further develop their ability to independently explore problems. Using state-of-the-art electronics and computers at the largest radio telescopes in the world, the students will gain confidence in their ability to tackle large and complex problems. Opportunities to collaborate with scientists in the U.S. and abroad and to report their work at conferences and in publications will enhance students' research experience and prepare them for graduate training or other roles in the technical workforce.