Neutron Stars, Electron Density Turbulence and Interstellar/Intergalactic Seeing

AST 0206036 cordesdr。康奈尔大学的James Cordes将领导一个多方面的项目，涉及中子星，脉冲星物理和种群，以及星际和星系间介质的探测。研究的主要领域是：*脉冲星天体测量使用甚长基线阵列（VLBA），阿雷西博望远镜，和绿岸望远镜（GBT）。目的是获得几十颗脉冲星的新的固有运动和视差。最终目标是利用这些测量来了解电子密度和磁场中的银河系结构，并利用脉冲星的速度来约束核心坍缩和伴随而来的不对称性的物理现象，这些不对称性给脉冲星带来了冲击。*在银河系中心搜索新的脉冲星，并搜索来自附近星系M33（使用阿雷西博）和M31（使用GBT）的单个分散脉冲。在这些星系中探测到多颗脉冲星，一旦我们的星系和宿主星系的视线测量被移除，就可以探测星系间介质。*改进银河电子密度模型和脉冲星距离尺度也是本项目的主要活动。科德斯博士将利用新的天体测量结果和多波长观测，在早期模型的基础上建立更详细的模型。还将根据无线电散射测量和发射测量对电子密度的波动进行建模。平均电子密度和波动电子密度的组合模型允许对广泛的可观测数据进行预测，包括那些描述星际闪烁和散射的数据。新的模型将特别适用于伽玛射线爆发余辉和日内可变活动星系核源的观测解释。*通过测量遥远脉冲星的脉冲宽度，Cordes博士将探索电子密度波动中微观结构的详细方面。“异常”频率尺度的证据表明，微观结构是各向异性和斑块的。*类似于星际散射，从星系间介质和向高红移活动星系核（AGN）方向移动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，并在观察中验证它们的存在。特别是，在HII区域冲击的再电离时期，可以检测到增强的散射。*科德斯博士将研究巨脉冲和其他可能具有理论和观测成分的无线电瞬变现象。将对已知脉冲星进行全面调查，以寻找从蟹状脉冲星中看到的巨大脉冲。他将寻求一个模型，将巨大的脉冲发射与某些脉冲星的外磁层联系起来，在那里可以满足回旋共振条件，并将巨大的无线电脉冲与x和x射线波段的高能量发射联系起来

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.***