# The Radius of PSR J0740+6620 from NICER and XMM-Newton Data

“The Radius of PSR J0740+6620 from NICER and XMM-Newton Data” (2021), by M. Coleman Miller et al. Physics and Astronomy research paper. Original abstract below, unchanged. A free PDF is available.

- Authors: M. Coleman Miller, Frederick K. Lamb, Alexander J. Dittmann, Slavko Bogdanov, Zaven Arzoumanian, Keith C. Gendreau, Sébastien Guillot, Wynn C. G. Ho, James M. Lattimer, Michael Loewenstein et al.
- Published: September 1, 2021
- Field: Physics and Astronomy
- DOI: https://doi.org/10.3847/2041-8213/ac089b
- Free PDF: https://arxiv.org/pdf/2105.06979

## 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 ±1 σ 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.

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