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J. Dittmann, A. Parthasarathy, C. B. Markwardt, C. L. Baker, E. Fonseca, F. K. Lamb, H. T. Cromartie, I. Cognard, I. Stairs, J. M. Lattimer, K. C. Gendreau, L. Guillemot, M. C. Miller, M. Kerr, M. Loewenstein, M. T. Wolff, P. S. Ray, S. Bogdanov, S. Guillot, S. Manthripragada, S. M. Morsink, S. Pollard, S. Ransom, T. Cazeau, T. Okajima, T. T. Pennucci, W. C. G. Ho, Z. Arzoumanian","submitted_at":"2021-05-14T17:33:32Z","abstract_excerpt":"PSR J0740$+$6620 has a gravitational mass of $2.08\\pm 0.07~M_\\odot$, 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, combine"},"claims":{"count":4,"items":[{"kind":"strongest_claim","text":"We find that the equatorial circumferential radius of PSR J0740+6620 is 13.7^{+2.6}_{-1.5} km (68%). When all measurements are included the radius of a 1.4 M_⊙ neutron star is known to ±4% and the radius of a 2.08 M_⊙ neutron star is known to ±5%.","source":"verdict.strongest_claim","status":"machine_extracted","claim_id":"C1","attestation":"unclaimed"},{"kind":"weakest_assumption","text":"The radius inference assumes specific geometries and temperature distributions for the rotating hot spots plus a particular model for the neutron-star atmosphere and beaming; if these are incorrect the reported credible intervals would shift.","source":"verdict.weakest_assumption","status":"machine_extracted","claim_id":"C2","attestation":"unclaimed"},{"kind":"one_line_summary","text":"PSR J0740+6620 has an equatorial radius of 13.7^{+2.6}_{-1.5} km, and multi-messenger data constrain 1.4 and 2.08 solar-mass neutron star radii to 12.45 and 12.35 km respectively.","source":"verdict.one_line_summary","status":"machine_extracted","claim_id":"C3","attestation":"unclaimed"},{"kind":"headline","text":"The highest-mass neutron star with a reliable radius measurement has an equatorial circumference of 13.7 km.","source":"verdict.pith_extraction.headline","status":"machine_extracted","claim_id":"C4","attestation":"unclaimed"}],"snapshot_sha256":"e37eda48c3188b8b6da01d1db8b182a4534562821e0093897f4e7895276bdf12"},"source":{"id":"2105.06979","kind":"arxiv","version":1},"verdict":{"id":"6c239ac9-cadf-4948-a1bb-77d8ac3f1e4f","model_set":{"reader":"grok-4.3"},"created_at":"2026-05-17T06:54:17.506067Z","strongest_claim":"We find that the equatorial circumferential radius of PSR J0740+6620 is 13.7^{+2.6}_{-1.5} km (68%). When all measurements are included the radius of a 1.4 M_⊙ neutron star is known to ±4% and the radius of a 2.08 M_⊙ neutron star is known to ±5%.","one_line_summary":"PSR J0740+6620 has an equatorial radius of 13.7^{+2.6}_{-1.5} km, and multi-messenger data constrain 1.4 and 2.08 solar-mass neutron star radii to 12.45 and 12.35 km respectively.","pipeline_version":"pith-pipeline@v0.9.0","weakest_assumption":"The radius inference assumes specific geometries and temperature distributions for the rotating hot spots plus a particular model for the neutron-star atmosphere and beaming; if these are incorrect the reported credible intervals would shift.","pith_extraction_headline":"The highest-mass neutron star with a reliable radius measurement has an equatorial circumference of 13.7 km."},"references":{"count":130,"sample":[{"doi":"","year":2017,"title":"P., Abbott , R., Abbott , 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