Integrated Modeling of X-ray Light Curves for Self-consistent Inference of Neutron Star Mass, Radius, and Multipolar Fields

The equation of state of neutron stars is one of the fundamental problems in astrophysics and a core science goal for NICER and future X-ray missions such as STROBE-X and eXTP. We explore the parameter space allowed by X-ray data of millisecond pulsars through X-ray light curve modeling with physically-motivated heated regions. Our study employs massively parallel, distributed Markov Chain Monte Carlo parameter inference and efficient photon ray tracing in curved spacetime for generalized hot spots originating from arbitrary multipolar fields. As a case study, we explore NICER data of PSR J0030+0451, which has indicated non-antipodal hotspots that are evidence for the existence of non-dipolar magnetic fields. Our previous studies showed that several different multipolar field configurations can acceptably reproduce the NICER bolometric X-ray light curve of PSR J0030+0451. This latest iteration of study introduces additional freedom for parameters into the models: the stellar mass, stellar radius, and observer’s angle. This expansion adds complexity to the problem, but allows for self-consistent determination of the magnetic field and fundamental neutron star parameters. Preliminary findings and upcoming steps in this investigation will be detailed and discussed.