Constraining the dense matter equation of state with new NICER mass-radius measurements and new chiral effective field theory inputs
Nathan Rutherford, Melissa Mendes, Isak Svensson, Achim Schwenk, Anna L. Watts, Kai Hebeler, Jonas Keller, Chanda Prescod-Weinstein, Devarshi Choudhury, Geert Raaijmakers, Tuomo Salmi, Patrick Timmerman, Serena Vinciguerra, Sebastien Guillot, James M. Lattimer
arXiv:2407.06790v1 Announce Type: new
Abstract: Pulse profile modeling of X-ray data from NICER is now enabling precision inference of neutron star mass and radius. Combined with nuclear physics constraints from chiral effective field theory ($chi$EFT), and masses and tidal deformabilities inferred from gravitational wave detections of binary neutron star mergers, this has lead to a steady improvement in our understanding of the dense matter equation of state (EOS). Here we consider the impact of several new results: the radius measurement for the 1.42$,M_odot$ pulsar PSR J0437$-$4715 presented by Choudhury et al. (2024), updates to the masses and radii of PSR J0740$+$6620 and PSR J0030$+$0451, and new $chi$EFT results for neutron star matter up to 1.5 times nuclear saturation density. Using two different high-density EOS extensions — a piecewise-polytropic (PP) model and a model based on the speed of sound in a neutron star (CS) — we find the radius of a 1.4$,M_odot$ (2.0$,M_odot$) neutron star to be constrained to the 95% credible ranges $12.28^{+0.50}_{-0.76},$km ($12.33^{+0.70}_{-1.34},$km) for the PP model and $12.01^{+0.56}_{-0.75},$km ($11.55^{+0.94}_{-1.09},$km) for the CS model. The maximum neutron star mass is predicted to be $2.15^{+0.14}_{-0.16},$$M_odot$ and $2.08^{+0.28}_{-0.16},$$M_odot$ for the PP and CS model, respectively. We explore the sensitivity of our results to different orders and different densities up to which $chi$EFT is used, and show how the astrophysical observations provide constraints for the pressure at intermediate densities. Moreover, we investigate the difference $R_{2.0} – R_{1.4}$ of the radius of 2$,M_odot$ and 1.4$,M_odot$ neutron stars within our EOS inference.arXiv:2407.06790v1 Announce Type: new
Abstract: Pulse profile modeling of X-ray data from NICER is now enabling precision inference of neutron star mass and radius. Combined with nuclear physics constraints from chiral effective field theory ($chi$EFT), and masses and tidal deformabilities inferred from gravitational wave detections of binary neutron star mergers, this has lead to a steady improvement in our understanding of the dense matter equation of state (EOS). Here we consider the impact of several new results: the radius measurement for the 1.42$,M_odot$ pulsar PSR J0437$-$4715 presented by Choudhury et al. (2024), updates to the masses and radii of PSR J0740$+$6620 and PSR J0030$+$0451, and new $chi$EFT results for neutron star matter up to 1.5 times nuclear saturation density. Using two different high-density EOS extensions — a piecewise-polytropic (PP) model and a model based on the speed of sound in a neutron star (CS) — we find the radius of a 1.4$,M_odot$ (2.0$,M_odot$) neutron star to be constrained to the 95% credible ranges $12.28^{+0.50}_{-0.76},$km ($12.33^{+0.70}_{-1.34},$km) for the PP model and $12.01^{+0.56}_{-0.75},$km ($11.55^{+0.94}_{-1.09},$km) for the CS model. The maximum neutron star mass is predicted to be $2.15^{+0.14}_{-0.16},$$M_odot$ and $2.08^{+0.28}_{-0.16},$$M_odot$ for the PP and CS model, respectively. We explore the sensitivity of our results to different orders and different densities up to which $chi$EFT is used, and show how the astrophysical observations provide constraints for the pressure at intermediate densities. Moreover, we investigate the difference $R_{2.0} – R_{1.4}$ of the radius of 2$,M_odot$ and 1.4$,M_odot$ neutron stars within our EOS inference.