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# X-ray Millisecond Pulsars in the Galactic Globular Clusters

• Author / Creator
Zhao, Jiaqi
• In this thesis we study X-ray millisecond pulsars (MSPs) in the Galactic globular clusters (GCs) to better understand the X-ray emission from them. We analyze 55 ks and 290 ks of Chandra X-ray observations of the clusters M13 and Omega Cen, respectively. We find confident X-ray counterparts to five of the six MSPs recently discovered in M13, while we place an upper limit of the X-ray luminosity for the sixth. We also find optical counterparts to two M13 pulsars, which are likely white dwarfs, using the Hubble Space Telescope. In addition, we detect X-ray counterparts to two newly found MSPs in the GC Omega Cen. We then compile previous X-ray studies of MSPs to present a comprehensive census of X-ray MSPs in 29 GCs, including 64 MSPs with detected X-ray luminosities and 111 MSPs with X-ray upper limits. We find most detected X-ray MSPs have luminosities between $\\sim 10^{30}$ erg s$^{-1}$ to $3 \\times 10^{31}$ erg s$^{-1}$ (0.3--8 keV). We estimate the total number of MSPs in 36 GCs based on the correlation between the number of MSPs and stellar encounter rate in GCs, and suggest that around 600 to 1500 MSPs exist in those GCs. Finally, we estimate the number of X-ray-detectable MSPs in the Galactic bulge, and suggest there are between 1--90 MSPs with $L_X > 10^{33}$ erg s$^{-1}$ and $\\sim$ 20--900 MSPs with $L_X > 10^{32}$ erg s$^{-1}$ in the bulge.

• Subjects / Keywords
Fall 2021
• Type of Item
Thesis
• Degree
Master of Science
• DOI
https://doi.org/10.7939/r3-d7xc-a167