Measuring the gravitational wave background using precision pulsar timing

We investigate the possibility of using high precision timing measurements of radio pulsars to constrain or detect the stochastic gravitational wave background (GWB). Improved algorithms are presented for more accurately determining the pulse times of arrival at Earth and characterizing pulse profile shape variation. Next, we describe the design and construction of a new set of pulsar backends based on clusters of standard personal computers. These machines, the Astronomy Signal Processors (ASPS), coherently correct the pulse broadening caused by interstellar plasma dispersion. Since they are based in software, they are inherently more flexible than previous generations of pulsar data recorders. In addition, they provide increased bandwidth and quantization accuracy. We apply these methods to 2.5 years worth of millisecond pulsar data recorded with the ASP systems at the Arecibo and Green Bank Telescopes, and present pulse profiles, dispersion measure variation, and timing model parameters derived from this data.;We then develop the theory of gravitational wave detection using pulsar timing, and show how data from several pulsars can be combined into a pulsar timing array for this purpose. In particular, a new method of accounting for the effect of the timing model fit on the gravitational wave signal is presented. This method incorporates the exact timing model basis functions without relying on Monte Carlo simulation. We apply this method to the 2.5 year dataset previously mentioned and derive a gravitational wave limit of hc(1 yr-1) < 2.46 x 10-14. Finally, we study the 20-year timing record of PSR B1937+21 and obtain information on how severely interstellar medium effects will compromise future GWB detection. We predict that these developments, in conjunction with historical data, could provide the first successful direct gravitational wave detection on a 5--10 year timescale.