2021/05/14 by M. C. Miller, F. K. Lamb, A. J. Dittmann +25 · 3 citations
Physics and Astronomy · #astro-ph.HE #gr-qc #nucl-ex #nucl-th
paper · pdf · doi:10.3847/2041-8213/ac089b
49 pages, 16 figures, submitted to The Astrophysical Journal Letters
arxiv created 2021/05/14 · arxiv updated 2021/09/29
PSR J0740+6620 has a gravitational mass of 2.08± 0.07~M_\odot, which is the highest reliably determined mass of any neutron star. As a result, a measurement of its radius will provide unique insight into the properties of neutron star core matter at high densities. Here we report a radius measurement based on fits of rotating hot spot patterns to Neutron Star Interior Composition Explorer (NICER) and X-ray Multi-Mirror (XMM-Newton) X-ray observations. We find that the equatorial circumferential radius of PSR J0740+6620 is 13.7+2.6-1.5 km (68%). We apply our measurement, combined with the previous NICER mass and radius measurement of PSR J0030+0451, the masses of two other ∼ 2~M_\odot pulsars, and the tidal deformability constraints from two gravitational wave events, to three different frameworks for equation of state modeling, and find consistent results at ∼ 1.5-3 times nuclear saturation density. For a given framework, when all measurements are included the radius of a 1.4~M_\odot neutron star is known to ± 4% (68% credibility) and the radius of a 2.08~M_\odot neutron star is known to ± 5%. The full radius range that spans the ± 1σ credible intervals of all the radius estimates in the three frameworks is 12.45± 0.65 km for a 1.4~M_\odot neutron star and 12.35± 0.75 km for a 2.08~M_\odot neutron star.