Southern Galactic Pulsars with MeerKAT

Pulsars are highly magnetised, rapidly spinning neutron stars. Their rotation is so stable that we use them as cosmic clocks for our experiments. Via the technique of pulsar timing, we model their spin down to every single rotation with microsecond precision. When found in binaries, we use timing to track and model their orbital motion. In the most compact systems, relativistic post-Keplerian corrections of the orbit can be modelled and measured, leading to tests of fundamental physics and measurements of the stellar masses. With 4,000 known pulsars, there are still many open questions about stellar mass distributions, condensed matter physics and binary evolution that can only be tackled via pulsar timing. In this thesis, I search and time pulsars with the new radio telescope MeerKAT, the most sensitive facility in the Southern Hemisphere. With is interferometric capabilities, I implement new techniques for the localisation and follow-up of new discoveries, and achieve the first science results including data from its newly installed S-band receivers. <br> The MPIfR-MeerKAT Galactic Plane Survey is a collaboration-led project. It implements accelerated Fourier-domain periodicity searches in a blind sky survey with the L-band, S-band and UHF MeerKAT receivers. In it, I have contributed to the discovery of 80+ new pulsars, followed up six binary discoveries, and successfully timed three. These are three millisecond pulsars in circular orbits with light helium white dwarf companions, two recycled pulsars in circular orbits with massive carbon-oxygen white dwarf companions, and a recycled pulsar in a double neutron star system. These discoveries will help tackle questions about the binary evolution and the mass distribution of white dwarf and neutron star masses. <br> Additionally, the timing of the double neutron star pulsar PSR J1208-5936 has led to a total mass measurement of 2.582 ± 0.006 solar masses, and individual mass measurements of 1.3 ± 0.3 solar masses. The system, with an orbital period of 0.632 days and an eccentricity of 0.348, is slanted to merge within 7.2 billion years due to the emission of gravitational-wave radiation, making it a progenitor of the neutron star merger events observed by ground-based gravitational-wave detectors. We have used this discovery and the performance of the survey at L-band to update the Galactic neutron star merger rate to 25⁺¹⁹/_-9 mergers per million years, consistent with previous estimates. <br> Finally, I have timed the massive pulsar white dwarf binary PSR J1227-6208 with joint MeerKAT and Murriyang observations dating up to 2011. Its companion is a massive oxygen-neon-magnesium white dwarf potentially close to the Chandrasekhar limit of 1.38 solar masses. Bayesian techniques were implemented to model the DM-induced red timing noise, leading to a companion mass constraint between 1.2 and 1.5 solar masses and confirming its massive nature. This is only the third mass measurement in this type of system, made possible only by the large sensitivity of MeerKAT.