Abstract
Pulsars are some of the most intriguing objects that we know of in the universe. It is difficult to visualize remnant cores of exploded massive stars that contain as much mass as our Sun, are the size of a small city, spin anywhere from a few times to a few hundred times per second and have some of the strongest magnetic fields in the known universe. These pulsars are excellent probes into the fundamental laws of physics that govern our universe and have been studied in a variety of wavelengths, mainly radio waves, X-rays and γ-rays. This dissertation explores pulsars and millisecond pulsars (MSPs) by searching γ-ray bright sources for new MSPs using radio observations and improving our γ-ray timing techniques to study radio-quiet pulsars.
In the second chapter, I explore γ-ray bright sources to search for new MSPs. To 0th order, the Fermi−Large Area Telescope (LAT) has linked γ-ray MSPs to radio detections, either via radio discovery and follow up γ-ray detections via LAT or vice versa. Fermi−LAT has additionally confirmed the dominant source of γ-ray emission within our Milky Way galaxy to be MSPs and several globular clusters (GCs) have been detected in γ-rays with 3 cluster MSPs confirmed to have γ-ray pulsations. Based on these connecting links, I conducted radio observations to search for new MSPs, using the Green Bank Telescope (GBT), on several γ-ray bright globular clusters. This work led to the discovery of PSR J1716−2808A, the first MSP in the globular cluster NGC 6316.
My third and fourth chapters focus on my work studying radio-quiet pulsars using a novel pulsar timing technique focused on optimizing timing analysis using individual γ-ray photons or “events”, aptly named event_optimize. Pulsar timing accounts for every rotation of the neutron star by measuring and modeling the arrival times of the pulses. In this dissertation, I focus predominantly on radio waves and γ-rays. Timing with γ-rays would require integrating several weeks or months of data due to the average γ-ray photon rate for most pulsars (<1 photon/day) with Fermi−LAT among a strong γ-ray background due to the diffuse Galactic emission. Integrating the photons over weeks to months into pulse profiles would average over various noise processes that exist on short timescales within our data and bake that noise into our measurements. One way to avoid this is by treating each photon as individual events in order to model those short timescale noise variations directly. I do this via Bayesian MCMC techniques in a process called single-photon timing. In Chapter 3, I report the proper motion, i.e. the transverse motion across the sky, of 12 radio−quiet pulsars, with 5 pulsars having significant detections and 3 pulsars show noteworthy associations or interesting features. In Chapter 4, I report the serendipitous discovery of the first exoplanet system around a young pulsar and explore the scenarios of the exoplanets either having formed post supernova or having survived the supernova.
Lastly, I conclude my work by providing updates on projects that are in progress and will be carried over during my post-doctoral position. I will provide updates on radio observations conducted on 27 Fermi−LAT unassociated sources, i.e. point-like sources detected by Fermi−LAT with unknown counterparts, to search for new γ-ray MSPs. Future applications of this dissertation that I will continue in my post-doctoral work include timing the remaining radio−quiet pulsars to measure their proper motion, improve our single photon timing software and identify any intriguing associations. It is likely that the only way to study the new serendipitous planets is through continued γ-ray timing with Fermi−LAT.
