Constraining neutron star properties with a new equation of state insensitive approach
B. Biswas, Sayak Datta
Abstract
Instead of parametrizing the pressure-density relation of a neutron star (NS), one can parametrize its macroscopic properties such as mass ($M$), radius ($R$), and dimensionless tidal deformability ($\mathrm{\ensuremath{\Lambda}}$) to infer the equation of state (EOS) combining electromagnetic and gravitational wave (GW) observations. We present a new method to parametrize $R(M)$ and $\mathrm{\ensuremath{\Lambda}}(M)$ relations, which approximates the candidate EOSs with accuracy better than 5% for all masses and spans a broad region of the $M\ensuremath{-}R\ensuremath{-}\mathrm{\ensuremath{\Lambda}}$ plane. Using this method we combine the $M\ensuremath{-}\mathrm{\ensuremath{\Lambda}}$ measurement from GW170817 and GW190425, and simultaneous $M\ensuremath{-}R$ measurement of pulsars PSR $\mathrm{J}0030+0451$ and PSR $\mathrm{J}0740+6620$ to place joint constraints on NS properties. At 90% confidence, we infer ${R}_{1.4}=12.0{5}_{\ensuremath{-}0.87}^{+0.98}\text{ }\text{ }\mathrm{km}$ and ${\mathrm{\ensuremath{\Lambda}}}_{1.4}=37{2}_{\ensuremath{-}150}^{+220}$ for a $1.4\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ NS, and ${R}_{2.08}=12.6{5}_{\ensuremath{-}1.46}^{+1.36}\text{ }\text{ }\mathrm{km}$ for a $2.08\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ NS. Furthermore, we use the inferred values of the maximum mass of a nonrotating NS ${M}_{\mathrm{max}}=2.5{2}_{\ensuremath{-}0.29}^{+0.33}\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ to investigate the nature of the secondary objects in three potential neutron star--black hole merger (NSBH) systems.