# Neutron Star Mass-Radius Constraints using Evolutionary Optimization

## by Abigail Stevens

Published November 24, 2016 in Science

Pizza talk at the Anton Pannekoek Institute for Astronomy, University of Amsterdam, on 24 November 2016.

The equation of state of cold supra-nuclear-density matter, such as in neutron stars, is an open question in astrophysics. A promising method for constraining the neutron star equation of state is modelling pulse profiles of thermonuclear X-ray burst oscillations from hotspots on accreting neutron stars. The pulse profiles, constructed using spherical and oblate neutron star models, are comparable to what would be observed by a next- generation X-ray timing instrument like ASTROSAT, NICER, or STROBE-X. In this talk, we showcase the use of an evolutionary optimization algorithm to fit pulse profiles to determine the best-fit masses and radii. By fitting synthetic data, we assess how well the optimization algorithm can recover the input parameters. Multiple Poisson realizations of the synthetic pulse profiles were fitted with the Ferret algorithm to analyze both statistical and degeneracy-related uncertainty, and to explore how the goodness-of-fit depends on the input parameters. For the regions of parameter space sampled by our tests, the mass and radius fits were accurate to ≤ 5%, with respective uncertainties of ≤ 7% and ≤ 10%.

This is my MSc research; the paper published on it, recently accepted for publication in ApJ, is available here: https://ui.adsabs.harvard.edu/#abs/2016arXiv160609232S/abstract