Determining neutron star masses and radii via analysis of NICER energy-resolved waveform data
Abstract
The masses and radii of neutron stars, if precisely and accurately known, would provide invaluable information about the properties of cold matter at several times nuclear saturation density. One promising way to obtain this information involves the analysis of the energy-resolved waveforms produced by hot spots on rotating neutron stars. Indeed, this is the prime method that will be used by the upcoming NASA mission NICER (Neutron star Interior Composition Explorer). We have developed sophisticated new Bayesian analysis methods that enable us to estimate quickly the masses and radii of rapidly rotating, oblate neutron stars using the energy-resolved waveforms of their X-ray burst oscillations and to determine the uncertainties in these mass and radius estimates. We find that fits to synthetic data that have realistic modulation amplitudes and total counts comparable to the number that could be obtained with NICER determine the gravitational mass M and the equatorial circumferential radius R_eq to within 3%-7% for rotation rates >300 Hz and spot and observer inclinations >60 degrees. We also find that fitting a model that assumes a uniform-temperature spot to waveforms generated using a spot in which the temperature varies with latitude by 25% does not significantly bias M and R_eq estimates. Thus, although more work needs to be done, this method appears to be relatively robust against systematic deviations from our model assumptions as well as being able to yield precise masses and radii for favorably oriented systems.
- Publication:
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American Astronomical Society Meeting Abstracts #225
- Pub Date:
- January 2015
- Bibcode:
- 2015AAS...22521409M