Impact of PREX-II and Combined Radio/NICER/XMM-Newton’s Mass–radius Measurement of PSR J0740+6620 on the Dense-matter Equation of State
B. Biswas
Abstract
Abstract In this paper, we discuss the impact of the following laboratory experiments and astrophysical observation of neutron stars (NSs) on their equation of state (EoS): (a) the new measurement of neutron skin thickness of 208 Pb, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>skin</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>208</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>0.29</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.07</mml:mn> </mml:math> fm by the PREX-II experiment; (b) the mass measurement of PSR J0740+6620 has been slightly revised down by including additional ∼1.5 yr of pulsar timing data. As well as the radius measurement of PSR J0740+6620 by joint NICER/XMM-Newton collaboration, which has a similar size to PSR J0030+0451. We combine this information using Bayesian statistics along with the previous LIGO/Virgo and NICER observations of NS using a hybrid nuclear+piecewise-polytrope EoS parameterization. Our findings are as follows. (a). Adding PREX-II result yields the value of empirical parameter <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>L</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>69</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>19</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>21</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> MeV, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>skin</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>208</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0.20</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.05</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.05</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> fm, and radius of a 1.4 M ⊙ ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1.4</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>12.75</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.54</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.42</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> km at 1 σ confidence interval. We find these inferred values are mostly dominated by the combined astrophysical observations as the measurement uncertainty in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>skin</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>208</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> by PREX-II is much broader. Also, a better measurement of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>skin</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>208</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> might have a small effect on the radius of low-mass NSs but, for the high masses, there will be almost no effect. (b) After adding the revised mass and radius measurement of PSR J0740+6620, we find the inferred radii of NSs are slightly pushed toward the larger values and the uncertainty on the radius of a 2.08 M ⊙ NS is moderately improved.