by Dr. Zhao Jiaqi (or Jake Zhao)
Thesis defended on August 6, 2025
Department of Physics, University of Alberta
Thesis advisor: Prof. Craig Henke
Abstract:
There is no doubt that the Universe is full of fascinating phenomena. The Chandra X-ray Observatory (Chandra), with its unprecedented angular resolution and sensitivity, has opened a new window for observing, studying, and appreciating the Universe in X-rays.
This thesis presents X-ray studies of millisecond pulsars (MSPs) in the globular cluster (GC) Omega Centauri (Omega Cen), diffuse X-ray emission from the GC Terzan 5, and a young neutron star (NS) in the supernova remnant Cassiopeia A (Cas A), utilizing Chandra datasets. We first search for X-ray counterparts to 18 MSPs newly discovered in Omega Cen. Using Chandra ACIS-I datasets with a total exposure time of 290.9 ks, we identify 11 confident X-ray counterparts to these MSPs, based on their positions, spectral properties, and X-ray colors. Additionally, we find clear correlations between the X-ray luminosities and minimum companion masses, as well as mass functions, of spider pulsars, and provide empirical fits to these relations. Next, we look into the diffuse X-ray emission from the field of Terzan 5, using deep Chandra ACIS-S observations with a total exposure time of 641.6 ks. We report the detection of a diffuse X-ray component genuinely associated with Terzan 5, and explore its possible nature through spectral analysis. Finally, we reexamine the rapid cooling of the Cas A NS utilizing newly obtained as well as archival Chandra HRC-S datasets. We detect significant declines in the surface temperature and X-ray flux of the NS, leading to an independent verification of its cooling rate. We also infer the maximal critical temperature of neutron superfluidity in the core of the Cas A NS.