Neutron Stars, Electron Density Turbulence and Interstellar/Intergalactic Seeing

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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.***