RUI: Pulsars and the Interstellar Medium

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Abstract Stinebring Turbulence in the interstellar medium provides the support needed to keep the gas from collapsing into a pancake. Evidence from pulsar observations indicates that a turbulent cascade of energy may exist over 12 orders of magnitude in scale size from 10 to the eighth (one hundred million) cm to 100 parsec. This turbulent cascade is not well understood, although high mass stars probably account for much of the energy input to the cascade through stellar winds, ionization, and supernova explosions. In particular, the dissipation of turbulent energy into heat at some scale size less than 10 to the tenth (ten billion) cm must occur, but the details of the mechanism and the physical conditions under which this happens are sketchy. The research to be carried out is aimed at determining the strength of the turbulent cascade at a size scale around 10 to the tenth cm and smaller and to learn more about the dissipation mechanism. The main technique employed will be the observational study of radio pulsar scintillation in the weak scattering regime. This is an opportune time to embark on such a study since both the upgraded Arecibo, Puerto Rico telescope and the soon-to-be-completed Green Bank Telescope will provide outstanding opportunities for pulsar observations above 1 GHz. This is the frequency range in which weak scattering phenomena can be studied effectively. The phenomenon of image-splitting, in which the pulsar image separates into two or more distinct pieces due to scattering in the transition regime between strong and weak scattering, will also be explored. The goals are the same: to better elucidate the strength of the electron inhomogeneity spectrum in the Galaxy and to seek evidence for a dissipation scale. High time resolution studies of bright pulsars will also be undertaken using a well-known VLBI recording system, the S2 system, to obtain baseband sampled data. These observations, which can be conducted at several observat ories (and observing frequencies) simultaneously, will allow high-precision monitoring of pulsar dispersion measures. This provides additional information about the electron inhomogeneities in the Galaxy. As a secondary effort, the baseband sampled data will also be analyzed to study brief and intense radio emission from pulsars in order to better understand the emission physics. Undergraduate students from Oberlin College will be centrally involved in all of these projects and will participate in observations, analysis, and the presentation of the results.