The Radius of PSR J0740+6620 from NICER and XMM-Newton Data
Guillemot, L.; Kerr, M.; Ray, P. S.; Wolff, M. T.; Guillot, S.; Miller, M. C.; Markwardt, C. B.; Ho, W. C. G.; Lamb, F. K.; Dittmann, A. J.; Bogdanov, S.; Arzoumanian, Z.; Gendreau, K. C.; Lattimer, J. M.; Morsink, S. M.; Okajima, T.; Stairs, I.; Cognard, I.; Fonseca, E.; Loewenstein, M.; Baker, C. L.; Cazeau, T.; Manthripragada, S.; Pollard, S.; Cromartie, H. T.; Parthasarathy, A.; Pennucci, T. T.; Ransom, S.
United States, France, Canada, Germany, Hungary
Abstract
PSR J0740+6620 has a gravitational mass of 2.08 ± 0.07 M⊙, 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 ${13.7}_{-1.5}^{+2.6}$ 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⊙ 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 ~1.5-5 times nuclear saturation density. For a given framework, when all measurements are included, the radius of a 1.4 M⊙ neutron star is known to ±4% (68% credibility) and the radius of a 2.08 M⊙ 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⊙ neutron star and 12.35 ± 0.75 km for a 2.08 M⊙ neutron star.