Neutron Star Parameter Constraints through Burst Spectral Analysis and Pulse Profile Modeling of Thermonuclear Oscillations

Thermonuclear X-ray bursts result from runaway nuclear fusion on the surfaces of accreting neutron stars. In some cases, coherent pulsations—known as burst oscillations—are observed in the light curves of these bursts. Despite being detected decades ago, the exact origin of these oscillations remains a mystery. Modeling the spectrum of these bursts alongside pulse profile modeling of the oscillations are two powerful methods for constraining the mass and radius of neutron stars. One fundamental assumption of burst spectral modeling is that the stellar surface emits uniformly. In this talk, I will discuss how the presence of undetected hot spots, particularly at the rotational poles, affects mass and radius estimates derived from burst spectral modeling. Furthermore, I will present recent findings on mass and radius constraints obtained through pulse profile modeling of burst oscillations. I will also explain how pulse profile modeling of burst oscillations can distinguish between the hot-spot and r-mode models, the two leading theories for the origin of thermonuclear burst oscillations.