Searching for pulsars in the Galactic centre and timing of a massive pulsar

Abstract

Pulsars are rotating neutron stars that emit pulsating signals. They serve as valuable tools for studying a wide range of topics, from general relativity to the interstellar medium. The discovery of a pulsar in the Galactic centre (GC) would be particularly fascinating due to its proximity to the Sgr A*, the black hole at the centre of our Galaxy. Such a discovery could provide insights into the local environment and the nature of the black hole itself. <br /> In the GC, up to 1000 pulsars were predicted, but thus far only six have been found, including a magnetar. One of the explanations is that the dense environment in the GC causes extreme interstellar scattering, reducing the sensitivity of pulsar surveys, particularly for short-period pulsars. To improve our sensitivity to long-period pulsars, a Fast Folding Algorithm (FFA) was used rather than the traditional Fast Fourier Transform (FFT). In this thesis, an FFA pipeline for accelerated pulsars was implemented for the first time to search for pulsars within 1° around GC using the data from the High Time Resolution Universe Pulsar Survey-South Low latitude. In this work, a new slow pulsar (PSR J1746-2829) was discovered with an angular distance of &#126; 0.5° from the GC. Follow-up observations revealed that this pulsar has properties that are usually associated with radio magnetars. Interestingly, there is another object in the GC that shows magnetar-like properties, in addition to the known magnetar. This may suggest that the GC has an anomalously large fraction of magnetars to non-recycled pulsars compared to the rest of the Galaxy. <br /> Extreme interstellar scattering can significantly reduce the sensitivity of pulsar surveys. Fortunately, the scattering time is decreasing with the fourth power of the observing frequency. As a result, the FFA pipeline for accelerated pulsars was modified to search for a high observational frequency (230 GHz) dataset from the three most sensitive stations from the Event Horizon Telescope observations of Sgr A* in 2017. This survey is the highest frequency pulsar survey to date, leading to negligible interstellar effects. However, pulsars have a steep spectrum, making them dimmer at higher frequencies, and harder to detect. We used the FFA and FFT with acceleration search pipelines to search for pulsars in this dataset, but no new pulsars were detected. The further empirical sensitivity analysis shows that we are only sensitive to less than 2% of the known pulsar population in this search, with less sensitivity on the slow pulsars, highlighting the need for FFA searches. <br /> Lastly, we continued the timing efforts for a massive pulsar-WDbinary system, PSR J0348+0432. In this work, the timing baseline was extended from 3 to 10 years, leading to improved constraints on the orbital period decay (<em>P_b</em>), which can be used to constrain both of the masses. We found that the <em>P_b</em> was significantly reduced compared to the predicted <em>P_b</em> from the mass measurements and orbital parameters from the previous work. I discussed various factors influencing <em>P_b</em>, such as a possibility of this system orbiting an unseen companion.