Neutron Stars, Electron Density Turbulence and Interstellar/Intergalactic Seeing

中子星、电子密度湍流和星际/星系间视宁度

• 批准号: 0206036
• 负责人: James Cordes
• 金额: $ 27万
• 依托单位: Cornell University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-07-01 至 2006-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0206036&HistoricalAwards=false
• 关键词: Neutron; Stars; Electron; Density; Turbulence

AST 0206036CordesDr. James Cordes of Cornell University will lead a multi-faceted project involving neutron stars, pulsar physics and populations, and probing of the interstellar and intergalactic media. The main areas of investigation are: * Pulsar astrometry using the Very Long Baseline Array (VLBA), the Arecibo Telescope, and the Green Bank Telescope (GBT). The intent is to obtain new proper motions and parallaxes of a few dozen pulsars. The ultimate goal is to use such measurements to understand Galactic structure in electron density and magnetic field, and also to use pulsar velocities to constrain the physics of core collapse and attendant asymmetries that give pulsars `kicks.' * Searches for new pulsars in the Galactic center and searches for individual dispersed pulses from the nearby galaxies M33 (using Arecibo) and M31 (using the GBT). Detection of multiple pulsars in these galaxies allows probing of the intergalactic medium once contributions to line-of-sight measures from our Galaxy and the host galaxy are removed.* Improving Galactic electron density models and the pulsar distance scale is also a majoractivity in this project. Dr. Cordes will build upon an earlier model by using new astrometry results and multi-wavelength observations that allow more detailed modeling. Fluctuations in electrondensity are also to be modeled, based on radio scattering measurements and emission measures. The combined model for the mean and fluctuating electron density allows predictions to be made for a wide range of observables, including those that describe interstellar scintillations and scattering. The new models will have particular application to interpretations of observations of gamma-ray burst afterglows and intra-day variable active galactic nuclear sources.* Through measurements of pulse broadening of distant pulsars, Dr. Cordes will explore detailed aspects of the microstructure in the electron density fluctuations. Evidence of `anomalous'frequency scaling suggest that the microstructure is anisotropic and patchy. * Analogous to interstellar scattering, propagation effects from the intergalactic medium andintervening galaxies looking toward high redshift active galactic nuclei (AGN) are within reach of VLBI observations. Dr. Cordes will model possible effects and test their presence in observations. In particular, enhanced scattering during the epoch of reionization from HII region shocks may be detectable.* Dr. Cordes will study giant pulses and possibly other radio transients with both theoreticaland observational components. A comprehensive survey of known pulsars for giant pulses likethose seen from the Crab pulsar will be made. He will pursue a model that ties giant-pulseemission to the outer magnetospheres of certain pulsars where a cyclotron resonance conditioncan be satisfied and which links giant radio pulses to high energy emission in the X-and--raybands.***

AST0206036CordesDr.康奈尔大学的詹姆斯·科德斯将领导一个多方面的项目，涉及中子星、脉冲星物理和种群，以及星际和星际介质的探测。主要研究领域是：*使用甚长基线阵列(VLBA)、阿雷西博望远镜和绿岸望远镜(GBT)的脉冲星天体测量。其目的是获得几十个脉冲星的新自行和视差。最终目标是利用这样的测量来了解银河系的电子密度和磁场结构，并利用脉冲星的速度来约束核心塌缩和伴随而来的给予脉冲星的不对称性的物理学。*在银河系中心搜索新的脉冲星，并从附近的星系M33(使用阿雷西博)和M31(使用GBT)搜索单个分散的脉冲。探测到这些星系中的多颗脉冲星后，一旦我们的星系和宿主星系对视线测量的贡献被剔除，就可以探测星际介质。*改进银河系电子密度模型和脉冲星距离标度也是这个项目的主要活动。科德斯博士将在早期模型的基础上，使用新的天体测量结果和多波长观测，从而建立更详细的模型。电子密度的波动也要根据无线电散射测量和发射测量进行建模。平均电子密度和波动电子密度的组合模型允许对广泛的观测数据进行预测，包括那些描述星际闪烁和散射的观测数据。新模型将特别应用于伽马射线爆发余辉和日内活动星系核源观测的解释。*通过测量遥远脉冲星的脉冲展宽，科德斯博士将探索电子密度波动中微观结构的详细方面。“异常”频率标度的证据表明，微结构是各向异性的和片状的。*类似于星际散射，来自星际介质和朝向高红移活动星系核(AGN)的星系的传播效应在VLBI观测范围内。科德斯博士将模拟可能的影响，并在观察中测试它们的存在。特别是，在HII区冲击的再电离时期，可能可以检测到增强的散射。*科德斯博士将研究巨型脉冲和可能具有理论和观测成分的其他射电瞬变。我们将对已知脉冲星的巨大脉冲进行全面调查，就像从Crab脉冲星看到的那样。他将寻求一个模型，将巨型脉冲发射与某些脉冲星的外层磁层联系起来，在那里可以满足回旋共振条件，并将巨型射电脉冲与X和射线波段的高能量发射联系起来。