X-ray modelling of accreting neutron stars

Neutron stars residing in binary systems can attract the outer gaseous layers of their companion star. As this material spirals towards the neutron star, it heats up and starts to emit in the X-ray band. However, material doesn't always reach the surface of the neutron star unencumbered: if the neutron star is sufficiently magnetic, its magnetic field may start to interact with the inflowing gas. Various odd types of behaviour may be the result: pulsations seen from the poles of the neutron star as material is magnetically channeled onto them; propeller-like outflows; or 'trapped-disks' where the inflowing gas gets stuck when it encounters the magnetic field. In much of my PhD work, I focused on understanding these interactions via different approaches to study of the X-ray emission: (1) reflection spectroscopy, where we treat the accretion flow as a funhouse mirror and try to deduce its properties from the manner in which it reflects light; (2) timing studies, where we search for pulses from the poles; and (3) high-resolution X-ray spectroscopy, searching for blueshifted signatures of outflowing material driven by, for instance, the propeller mechanism.