Exploring pulsar-black hole binaries using the next generation of radio telescopes

• Main Author: Liu, Kuo
• Other Authors: Kramer, Michael; Stappers, Benjamin
• Published: University of Manchester 2012
• Subjects: 523.84425
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.553435

Binary pulsars are well known for their usefulness in testing gravitational theories. Pulsar-black hole (PSR-BH) binary systems, once discovered, will be the 'next generation of celestial laboratories' being able to both probe BH properties and test gravity especially General Relativity's cosmic censorship conjecture and no-hair theorem. The achievement of these prized goals requires highly precise pulsar timing observations, which are more readily achieved with the next generation of radio telescopes such as the Square Kilometre Array (SKA) and the Five-hundred-metre Aperture Spherical Radio Telescope (FAST). The purpose of work carried out in this thesis is to investigate the limits on precision timing and to explorethe potential for tests of theories of gravity by PSR-BH binaries with the future telescopes. Millisecond pulsars (MSPs) are more stable timers compared with normal pulsars. While the precision of MSP timing with present hardware is mainly limited by radiometer noise, for the brightest few MSPs one can already notice effects from other aspects, which can be separated into three categories: intrinsic noise from the pulsar, variations of the interstellar medium (ISM) effects, and instrumental artefacts. The case study based on the brightest MSP, PSR J0437-4715, demonstrates that most instrument-associated uncertainties in pulse time-of-arrival (TOA) measurement can be corrected by state-of-the-art techniques. The influence on TOAs by the interstellar medium (ISM) is shown to be unimportant for the source, and can potentially be corrected by approaches which are being developed. The TOA uncertainties for most MSPs observed with the next generation of radio telescopes, will mainly be limited by pulse jitter and radiometer noise. Based on this result, it is predicted that for normal-brightness MSPs a TOA precision of between 80 and 230 ns can be achieved at 1.4 GHz with 10-minute integrations by the SKA. With the current sensitivity, a further investigation on pulse jitter has been performed, regarding both the shape and central phase variability of several MSPs. No significant shape changes within a few hours observing time have been detected based on 10 to 100 s integrations. For PSR J0437-4715 the jitter parameter is quantified as f_J = 0.067+-0.002, based on timing on short timescales. Potential instrumental effects on this measurement have also been demonstrated. Jitter noise is found to be independent of observing frequency and bandwidth around 1.4 GHz on frequency scales of < 100 MHz, suggesting that the resulting uncertainty might not be mitigated by extending the observing bandwidth. Through detailed simulations, it has been found that timing a pulsar in orbit around a stellar mass BH (SBH) binary system with the next generation of radio telescopes can lead to a high precision determination of the BH mass and spin in ten years. Especially for MSPs, the measurements of mass and spin can be allowed for wide orbits of orbital period up to roughly ten days. The constrain on BH quadrupole moment is possible only with timing precisions achievable with MSPs, and for systems of either high-mass (e.g. ~80 solar mass) SBH or high orbital eccentricity. Meanwhile, timing a normal pulsar orbiting around the Galactic Centre BH, Sgr A*, with the SKA would lead to the extraction of the BH mass, spin and quadrupole moment within five years. Considering the perturbation from other stellar masses in the Galactic Centre region, these measurements could be converted to a test of the no-hair theorem with ~1% precision.