The Radius of PSR J0740+6620 from NICER and XMM-Newton Data
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, Sharon M. Morsink, Paul S. Ray, M. T. Wolff, C. L. Baker, T. Cazeau, Sridhar Manthripragada, C. B. Markwardt, Takashi Okajima, S. Pollard, I. Cognard, H. Thankful Cromartie, Emmanuel Fonseca, L. Guillemot, M. Kerr, A. Parthasarathy, Timothy T. Pennucci, S. M. Ransom, I. H. Stairs
Abstract
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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>13.7</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.5</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.6</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> 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.