Model-based exploration of pulse profile evolution in the X-ray binary Pulsars of the Small Magellanic Cloud.

Model fitting with our multi-satellite library of X-ray pulse-profiles, derived from all available pointed X-ray observations of the Small Magellanic Cloud (e.g. RXTE-PCA, Chandra ACIS, XMM, NuStar, NICER, Suzaku etc.), provides a new toolset to investigate accretion physics. To each pulse profile we fit a geometric model that incorporates fan-like and pencil-like X-ray emission from both poles, and includes gravitational light-bending. By modeling pulse-profiles for the same pulsar on many different occasions, over its full range of luminosity we can quantify and track changes in pulse shape, and look for what is driving these changes. In parallel, we track energy dependence of the pulse profile, spectral energy distribution, and accretion torques. Leveraging modeling and big data provide a route to measure fundamental neutron star properties, such as magnetic field strength and orientation. Community resources including the library itself, and an interactive modeling interface are being developed as part of this project.