RUI: Radio Astronomical Investigations of the Interstellar Medium, Relativistic Gravitation, and Pulsars

Carleton College, Northfield MN

Investigators

Abstract

Here, Dr. Weisberg will undertake a radioastronomical research program encompassing three major themes. The first two use pulsars as tools for the study of other physical phenomena - namely the interstellar medium and relativistic gravitation. The third focuses on studying the emissions and evolution of pulsars themselves. Pulsars possess several unique properties that make them ideal probes of the interstellar medium. Specifically, their emissions are pulsed, polarized, and pointlike. Their pulsing allows for dispersion delays to be measured, which leads to interstellar electron density determinations. Their high polarization permits the measurement of Faraday rotation, which yields galactic magnetic field measurements along the line of sight. That they are pointlike ensures that the signal probes a needle-thin column along the line of sight. In this part of the project, five principal spectrometric and polarimetric investigations will be undertaken that take advantage of these three properties to advance the understanding of a wide variety of phenomena in the interstellar medium, including the characteristics of neutral atomic, molecular, and ionized regions, especially on the smallest scales The first binary pulsar, PSR B1913+16, has proved to be an outstanding laboratory for the study of relativistic gravitation. Although the accuracy of probing gravity wave emission is now limited by systematic effects, there are still new and interesting relativistic phenomena that will be studied here. The 'Shapiro' gravitational propagation delay is expected to become measurable over the next decade, which will lead to two additional relativistic tests which can constrain otherwise viable gravitational theories. The 'geodetic' spin axis precession causes the line of sight to slowly drift across the pulsar, thereby permitting a rare glimpse of the emission beam in the direction orthogonal to its usual presentation. The additional observations which are supported here will uniquely help to further constrain the beam shape, a basic quantity that will be useful for emission mechanism studies. The details of the pulsar emission mechanism and of the nature of pulsar interiors are still unclear forty years after the discovery of these objects. A series of experiments to measure their polarized emissions will be carried out by Dr. Weisberg and students with an eye toward establishing the beam geometry, and studying and creating empirical emission models. The observations will be carried out with the Arecibo, Green Bank, and Parkes telescopes. Carleton College undergraduate students will be integrally involved in all aspects of data acquisition and analysis, including participation in two month-long trips to the Australia Telescope National Facility.