An XMM search for quiescient low-mass X-ray binaries in globular cluster using X-ray spectral identification

Low-mass X-ray binaries (LMXBs) are now routinely used for neutron star (NS) radius measurements. Observations of these systems in their quiescent stage (qLMXB) is one method leading to precise measurements. However, the dominant source of uncertainty on the NS radii remains the distance to the binary systems. Globular clusters (GCs) are therefore the places to look for more qLMXBs, due to their known or measurable distances and their abundance of binary systems. This thesis reports the discovery of seven candidate qLMXBs in six GCs, using observations from the XMM-Newton satellite, based on X-ray spectral consistency with NS hydrogen atmosphere models. The goal of this program of observations is to increase the population of known GC qLMXBs, for which longer follow-up exposures will permit high precision radius measurements. Nine candidates were initially identified based on their X-ray spectra with signal-to-noise ratio S/N > 3. Two candidates in NGC 6304 were tentatively confirmed, with consistent best-fit parameters, in a follow-up Chandra observation. One low-S/N candidate in NGC 6540 (S/N = 7) was subsequently excluded by a deeper, higher S/N (S/N = 17) observation. One other candidate was also excluded on the basis of the spatial velocity of the associated companion star, precluding cluster membership. Thus, the present work has added seven new qLMXB candidates to the eleven previously known.