High Precision Dual Frequency Timing of Millisecond Pulsars

Citation

Sandhu, Jagmit Singh (2001) High Precision Dual Frequency Timing of Millisecond Pulsars. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/17DD-8X47. https://resolver.caltech.edu/CaltechETD:etd-09172008-084556

Abstract

The science of precision millisecond pulsar timing can yield the most precise astrometric measurements ever made. This potential can only be realized through an extraordinary amount of investment in the experimental apparatus, the effort of many observers, and the close attention to details required to avoid the many pitfalls along the way. This thesis describes the work and results from a precision timing project aimed at monitoring the brightest millisecond pulsar, PSR J0437-4715. This pulsar is a very suitable target for such a study because of its small period (5.75 ms), low DM (2.69 pc cm⁻³), and high flux density (~ 90 mJy at 1.4 GHz). The initial work for this thesis involved completion and installation of the Fast Pulsar Timing Machine (FPTM) at Parkes observatory, Australia. With a bandwidth of 128 MHz and time resolution of 4 µs, this machine made a quantum jump in the time of arrival precision for PSR J0437-4715. The precision improved from ~ 2 µs to ~ 0.2 µs. In order to further enhance the signal-to-noise ratio achievable with this pulsar and probe the limits of precision pulsar timing, we have subsequently improved the FPTM significantly by doubling its bandwidth, so that it can record the pulsar radio emission over a 256 MHz bandwidth. This required us to double the IF processing hardware in the FPTM and implement numerous software modifications to control the observing apparatus, interface the FPTM with the observatory control computers, as well as process the data to produce final times of arrival.

Integration of just a few minutes with the 64 m Parkes radio telescope yield times of arrival for PSR J0437-4715 with a precision of 100 nanoseconds. The longer term residuals (3 years) show root-mean-square deviations of 500 nanoseconds. This excessively large scatter in the residuals has been traced to inaccurate polarization calibration, and a systematic quadratic trend of ~ 5 µs in the times of arrival as a function of baseband frequency. The latter phenomenon has been simulated in software and shown to arise from the large dynamic range in the baseband spectrum. Despite the systematic errors, our measurement of the pulsar's astrometric and binary parameters match the best obtained so far with other millisecond pulsars. This has allowed us to measure the pulsar's parallax, and the secular change in the binary's projected semi-major axis due to the system's proper motion. The latter effect restricts the inclination angle of the binary, i < 43°. The parallax, along with the period derivative and orbital period derivative, enable us to constrain the distance of the pulsar, 162 < d < 205 pc. A stability analysis of the pulsar's time of arrival residuals demonstrates that it matches the long term stability of the best studied millisecond pulsars, PSRs B1937+21 and B1855+09, at least on the time scale of the data available so far, 3 years. The precision in the pulsar position now matches the amplitude of the modulation of position expected from the pulsar's binary motion. Detection of this effect will require reduction of the calibration and spectral shape errors, as well as further refinements in the timing software used. Along with radio interferometric observations of the pulsar and optical detection of the white-dwarf companion, the pulsar timing position will provide the best contraints for frame tie between the ecliptic and extragalactic reference frames.

Thesis Files